Florentin Paris
email: florentin.paris@orange.fr.

Merrell A Miller

Sa'id Al-Hajri

Jan Zalasiewicz

Ancyrochitina Erichseni Sommer

Van Boekel

Ancyrochitina Fragilis Eisenack

Ancyrochitina Longispina Achab

Ancyrochitina Magna Nestor

Ancyrochitina Merga Jenkins

Porrectaspinosa Nestor

Ancyrochitina Ramosaspina Nestor

Al Hajri

Clathrochitina Sylvanica Jenkins

Conochitina Alargada Cramer

Conochitina Campanulaeformis Eisenack

Nestor

Cutichitina Legrandi Achab

Asselin Soufiane

Butcher, Mikulic Kluessendorf

Plectochitina Concinna Achab

Diez

Sphaerochitina Lepta Jenkins

Ancyrochitina Obesa Tsegelnjuk

ÔØ Å ÒÙ× Ö ÔØ Early Silurian chitinozoans from the Qusaiba type area, North Central Saudi Arabia

Keywords: crassicarinata sp. nov., Armoricochitina, Plectochitina lucasi sp. nov., and Spinachitina Chitinozoans, Biostratigraphy, Systematics, Palaeoenvironments, early Silurian, Saudi Arabia, Northern

Sixty one core samples from three shallow core holes penetrating the Qalibah Formation (Qusaiba Member) in North Central Saudi Arabia were investigated. These core slabs corresponding to grey-greenish hemipelagic shale or silty-shale yield well-preserved and very abundant early Silurian chitinozoans. Most of the recorded chitinozoan assemblages are diverse and include several new species occurring with wellknown species. An informal early Rhuddanian chitinozoan assemblage dominated by Cyathochitina caputoi is documented in the lowermost part of the Qusaiba Member. The six chitinozoan biozones defined above this basal assemblage range from Aeronian to Telychian.

They are considered of regional value for northern Gondwana. From the lowest to the highest they are the Angochitina qusaibaensis (pro parte), Conochitina alargada, Angochitina the chitinozoans (isolated vesicles, chain-like structures, clusters, coprolites) and their environmental context are briefly discussed.

Fifteen new species are described and illustrated: Ancyrochitina alhajrii sp. nov.,

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M A N U S C R I P T hemeri, Angochitina macclurei, Tanuchitina obtusa and Euconochitina silurica biozones. The older regional biozones have been previously documented in Saudi Arabia whereas the two youngest ones, the eponymous index species of which were described from the subsurface of the Algerian Sahara, are documented for the first time in the Arabian Peninsula. Four subbiozones, of at least of regional application, are also defined in order to improve the precision of biostratigraphic correlation between Silurian lithostratigraphic units cropping out along the Arabian Shield and their counterparts in the subsurface of Central Saudi Arabia.

Thanks to closely spaced and to regular sampling, the total range of several highly diagnostic forms as well as the interval of uncertainty between the successive chitinozoan biozones are better constrained. A hiatus with a duration of late Rhuddanian to early Aeronian separates the lowest informal chitinozoan assemblage from the qusaibaensis Biozone. A recent detailed study of the graptolites in the three cored holes provides independent chronostratigraphical control calibrating the previous chitinozoan-based age assignments. The qusaibaensis (pro parte), the alargada, and the hemeri chitinozoan biozones occur with the mid Aeronian convolutus graptolite Biozone whereas the macclurei chitinozoan Biozone extends through the early Telychian guerichi and turriculatus graptolite biozones. The obtusa and the silurica chitinozoan biozones occur in an interval devoid of usable graptolites. They are referred to the mid-late Telychian as they do not contain typical Sheinwoodian species.

Beside abundant chitinozoans and acritarchs, sporadic occurrences of scolecodonts and of eurypterid cuticle fragments are also noted in the organic residues. The presence of eurypterids reflects a shallowing trend in the sedimentary record, which is consistent with the distribution of the graptolites remains (siculae and/or rhabdosomes). Indeed, graptolites are common throughout the Qusaiba Member, except in the youngest processed samples presaging the shallower environments prevalent in the Sharawra Member. The taphonomy of A C C E P T E D M A N U S C R I P T

Introduction

Under the auspices of the Commission Internationale pour l'étude de la Microflore du Paléozoïque (CIMP) a multi-disciplinary project with Saudi Aramco was initiated in the early 1990s for documenting organic-walled microfossils and biostratigraphy from the Ordovician and Silurian formations from Saudi Arabia. One of the goals was to develop a robust regional chitinozoan biozonation allowing correlation between the strata exposed along the margin of the Arabian Shield and the Early Palaeozoic units including source rocks and reservoirs buried beneath a Mesozoic and Cenozoic cover in central and southern Saudi Arabia (Fig. 1a).

The first step is to establish and calibrate the chitinozoan biozones from the type areas of the

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Ordovician and Silurian formations and members exposed in the north-western part of Central Saudi Arabia. In Saudi Arabia, as in most of the tropical and sub-tropical desert regions, deep surficial weathering affects much of the exposed sedimentary rocks. This weathering proved to be responsible for the partial to total destruction of organic-walled microfossils and of the amorphous organic matter. In order to overcome this weathering phenomenon, shallow cores were drilled in the type area of the Qusaiba Member of the Qalibah Formation. They have been sampled and studied for the chitinozoans and other organic-walled microfossils (see this volume).

As far as chitinozoans are concerned, the Qalibah Formation is the most extensively investigated among the Saudi Arabian Early Palaeozoic lithostratigraphic units. The data are available in the following papers [START_REF] Mcclure | Chitinozoan and acritarch assemblages, stratigraphy and biogeography of the Early Palaeozoic of Northwest Arabia[END_REF][START_REF] Aoudeh | Regional distribution and chronostratigraphy of the Qusaiba Member of the Qalibah Formation in the Nafud Basin, Northwestern Saudi Arabia[END_REF][START_REF] Paris | Belonechitina arabiensis[END_REF][START_REF] Paris | New chitinozoan species from Llandoverian subsurface strata of Saudi Arabia[END_REF]Al-Hajri and Paris, 1988;[START_REF] Paris | Aeronian and Telychian chitinozoans from Central Saudi Arabia[END_REF] as well as an unpublished thesis [START_REF] Al-Hajri | Systematics and biostratigraphy of Middle Ordovician to Lower Silurian chitinozoans of the Arabian Peninsula[END_REF] and numerous Saudi Aramco internal reports (more than 300 internal reports). The goal of the present study is to refine the northern Gondwana chitinozoan biozonation based on the Saudi Arabian collections with the introduction of new biozones and subbiozones applicable to the Arabian palaeoplate.

Graptolites present in part of the section investigated [START_REF] Zalasiewicz | Early Silurian (Llandovery) graptolites from Central Saudi Arabia: first documented record of Telychian faunas from the Arabian Peninsula[END_REF] give precise ties with the standard graptolite biozones) and consequently with the series and stages of the standard Silurian chronostratigraphy [START_REF] Zalasiewicz | Early Silurian (Llandovery) graptolites from Central Saudi Arabia: first documented record of Telychian faunas from the Arabian Peninsula[END_REF][START_REF] Zalasiewicz | Graptolites in British stratigraphy[END_REF] In addition, because the recorded material is abundant and very well-preserved, the present investigations provide helpful information about intraspecific morphologic variations of several critical species, especially for the index species of previously and newly identified biozones and subbiozones. The generally close sampling and the partial overlap of the three selected boreholes help refining of the ranges of the most significant index species.

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1-3). In general samples are grey to greenish or grey-greenish shale. Slight lithological variations are recognized for example in the lowermost part of the Qusaiba-1

(carbonaceous shale from 256.4 ft to 254.8 ft) and silty shale intervals in the upper part of the Qusaiba-1 (136.5 ft to 132.05 ft) and in the Baq'a-3 core holes (cores 25 and 27).

These lithological variations indicate shallowing of the palaeoenvironments. In the upper sample (core 14) from the Baq'a-3 well this shallowing trend is more conspicuous and announces the boundary between the Qusaiba and the Sharawra members. A significant increase of eurypterid cuticle fragments, and possibly of plant remains, confirms this shallowing trend in the upper part of the Baq'a-3 core hole (cores 14 to 21; Table 2). A concomitant disappearance of the graptolites is noted in these more shallow environmental settings (Tables 1 and3). It is noteworthy that graptolites are not documented from the Sharawra Member (Al-Hajri and Paris, 1998, and unpublished data).

The absence of well-developed early Silurian black shale facies in the investigated cores is stressed. The only significant gamma ray peak is located at the carbonaceous shaly level at 254.8 ft in the Qusaiba-1 core hole. This thin interval (possibly condensed) in the lowermost part of the Qusaiba Member (see Melvin, this volume) yields lowermost Rhuddanian chitinozoans in great abundance (Fig. 6; Table 19). This chitinozoan assemblage, discussed in detail in Paris et al. (this volume), occurs below a hiatus (gap) that separates these Rhuddanian deposits from the mid-Aeronian graptolitic shale.

Technical procedure 2.2.1. Bedding plane observations

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All of the samples were examined using a binocular microscope at low to medium magnification (16 x or 40 x) prior to the crushing of the rock sample. The bedding plane surfaces of the core slab were wetted with alcohol in order to increase the contrast and to more easily recognize macrofossils and small organic remains. These observations revealed the occurrences of inarticulate brachiopods, ostracods and graptolites (siculae and rhabdosomes). Microfossils and larger organic-walled fossils, i.e. scolecodonts, plant, fragments, eurypterid cuticles and chitinozoans (as isolated vesicles, catenary structures, clusters and even coprolites comprised of crushed chitinozoans) were present with minerals (e.g., pyrite, heavy minerals, graphite) (Tables 123). The observation of the rock samples revealed that organic-walled microfossils are frequently concentrated on very thin darker bedding plane surfaces.

Acid treatment and microfossil sorting

The procedure described by [START_REF] Paris | Les chitinozoaires dans le Paléozoïque du sud-ouest de l'Europe (Cadre géologique -Etude systématique -Biostratigraphie)[END_REF][START_REF] Paris | Chitinozoans: a fascinating and mysterious microfossil group. Technical-card and direction for use[END_REF] for the isolation and preparation of chitinozoans was used. The technique is based on handpicking of all, or more frequently of a measured percentage of the specimens present in the palynological residue. The picking under a stereoscopic binocular microscope is accomplished using a finely drawn glass micropipette. After sorting a quantified fraction (depending on the abundance of the recovered chitinozoans) or the entire chitinozoan population from the residue of a sample, the picked vesicles are mounted as permanent palynological slides in Canada balsam. The identification of the species and counting of the specimens is made using these slides, whereas the best-preserved or the most significant individuals are separately prepared for SEM examination. After SEM observations and photomicrography, these individuals are also mounted as permanent palynological slides in Canada balsam according the technique described in [START_REF] Paris | Apports du microscope électronique à balayage dans l'étude des chitinozoaires opaques[END_REF]. This allows a secure preservation of the type material and

A C C E P T E D M A N U S C R I P T illustrated individuals. Moreover it is possible to precisely relocate these specimens in the palynological slides with England Finder coordinates (see captions of . In some cases (e.g., very abundant chitinozoans; new species) additional slides of selected specimens are prepared also.

Specimen counting and repository

Chitinozoans were too numerous in some samples for a complete inventory of all specimens (e.g. more than one thousand specimens per gram of rock in samples from 254.80 ft and 140.10 ft in Qusaiba-1, 289.1ft in Baq'a-3, and 261.2 ft in Baq'a-4). In such very rich residues, the picking and the counting were made from 20%, 10% or even 2 % of the residue (Tables 123). The chitinozoan abundance is expressed as number of specimens per gram of rock (Figs. [6][7][8]. The relative frequency (as a percentage) was calculated for each identified chitinozoan taxon and for undetermined specimens. The relative abundances and the stratigraphic ranges for each species recorded for the three investigated wells are given on these range diagrams. All of the palynological preparations, including those with the illustrated material, are stored in the collections of Geosciences/OSUR (CNRS, Observatoire des Sciences de l'Univers de Rennes) at the University of Rennes (France) under the repository numbers IGR 72201 to 72300 for the Qusaiba-1 core hole, IGR 72301 to 72346 for the Baq'a-3 core hole and 72351 to 72376 for the Baq'a-4 core hole. These palynological slides and the corresponding SEM photos are registered in the "CHITINO_IGR" and in the "PHOTOCHITINO" databases of F. Paris.

Chitinozoan biostratigraphy

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The proposed biozones and subbiozones are based on the First Appearance Datum (FAD) of selected index taxa or on the total range of the index species. This local biozonation is correlated with the regional Silurian chitinozoan zonation published by [START_REF] Paris | New chitinozoan species from Llandoverian subsurface strata of Saudi Arabia[END_REF] for Saudi Arabia. The chronostratigraphical age assignment is based on the graptolite zonation provided by the well-preserved, numerous, but often low diversity graptolite assemblages [START_REF] Zalasiewicz | Early Silurian (Llandovery) graptolites from Central Saudi Arabia: first documented record of Telychian faunas from the Arabian Peninsula[END_REF] present with the chitinozoans in many samples from the Qusaiba-1, Baq'a-3 and Baq'a-4 cores. Calibration of the Saudi Arabian regional chitinozoan biozonation of [START_REF] Paris | New chitinozoan species from Llandoverian subsurface strata of Saudi Arabia[END_REF] and correlation with the global Silurian chitinozoan zonation of [START_REF] Verniers | A global Chitinozoa biozonation for the Silurian[END_REF] are significantly improved in terms of standard graptolite zones. The precision of these graptolite/chitinozoan biozones ties is comparable to that published by [START_REF] Loydell | Integrated biostratigraphy of the lower Silurian of the Aizpute-41 core, Latvia[END_REF][START_REF] Loydell | Integrated biostratigraphy of the lower Silurian of the Ohesaare core, Saarema, Estonia[END_REF][START_REF] Loydell | Integrated biostratigraphy of the lower Silurian of the Kolka-54 core, Latvia[END_REF] for the Silurian of the Baltic area.

The average sampling interval is less than 6 ft in the Qusaiba-1 well (Table 1; Fig. 3). In the two Baq'a core holes it is approximately 20 feet (Tables 23; Figs. [4][5] and is too large for an exact location of the FADs and LADs of the selected index species. This introduces intervals of uncertainty of a few meters thickness. Additional regional control on the respective range of the species is possible because the stratigraphic intervals investigated in the three shallow cores partly overlap those studied previously in the deep boreholes of Central Saudi Arabia e.g., UDYN-1, TINT-2, NYYM-2 [START_REF] Paris | Final report on chitinozoans from well UDAYNAN. 1[END_REF][START_REF] Paris | Final report on the chitinozoans recorded in well TINAT[END_REF][START_REF] Paris | New chitinozoan species from Llandoverian subsurface strata of Saudi Arabia[END_REF] and ISWH EW-9 [START_REF] Paris | Final report on chitinozoans from well ALISAWYIAH EW-9[END_REF] (see Fig. 1a). Some of the taxa reported in open nomenclature or as nomina nuda in previous internal reports for Aramco [START_REF] Paris | Final report on chitinozoans from well UDAYNAN. 1[END_REF][START_REF] Paris | Final report on the chitinozoans recorded in well TINAT[END_REF][START_REF] Paris | Final report on chitinozoans from well ALISAWYIAH EW-9[END_REF][START_REF] Paris | Ranges and abundances of early Silurian chitinozoans in Qusaiba-1 shallow core (NE Saudi Arabia)[END_REF][START_REF] Paris | High resolution biostratigraphy of early Silurian chitinozoans in Baq'a-3 and no. 4 shallow cores (NE Saudi Arabia)[END_REF] are formally described and biostratigraphically constrained here. [START_REF] Mcclure | Chitinozoan and acritarch assemblages, stratigraphy and biogeography of the Early Palaeozoic of Northwest Arabia[END_REF] and

Al [START_REF] Al-Hajri | Systematics and biostratigraphy of Middle Ordovician to Lower Silurian chitinozoans of the Arabian Peninsula[END_REF] have already illustrated several of these new species. The abundant populations recovered allowed a biometric evaluation of vesicle dimensions (Tables 4-18,

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Figs. [10][START_REF]Three dimensional vesicle with the carina near the equator of the chamber and the small disc-like operculum[END_REF][12][START_REF] Belonechitina | [END_REF][14][15][16][17][18][19][20][21][22][23][24]).

The regional biozones and their subbiozones are defined and discussed in ascending stratigraphic order. Previously used chitinozoan biozone names are favoured. They are documented from diverse and abundant chitinozoan populations (usually more than 100 chitinozoans per gram of rock, and in a few cases more than 1000 individuals per gram of rock). The percentage of the indeterminate specimens is fairly low (usually less than 20% of the populations).

"Assemblage 1"

This chitinozoan assemblage is restricted to the lowermost part of the Qusaiba-1 core hole (core 27 at 256.4 ft, 255.15 ft and 254.8 ft; see Figs. 3 and 6) of the Qusaiba Member of the Qalibah Formation. It is only briefly mentioned here because it is defined elsewhere in this volume when documenting the boundary between the Sarah and the Qalibah formations in the Qusaiba-1 core hole (Paris et al., this volume). Cyathochitina caputoi (see Paris et al.,this volume;pl. VI,5) dominates this low diversity assemblage but with extremely high chitinozoan abundance in the dark carbonaceous shale at 254.8 ft (more than 9000 chitinozoans per gram of rock). Belonechitina pseudarabiensis (see Paris et al. this volume;pl. VI,figs. 6,[9][10] is another important species of this "assemblage 1" (sensu Paris et al., this volume) as it occurs in the lower Rhuddanian of Jordan [START_REF] Butcher | Early Llandovery chitinozoans from Jordan[END_REF], and is associated with very abundant Cyathochitina caputoi in the Nseirat section in Mauritania [START_REF] Al-Hajri | Age and palaeoenvironment of the Sharawra Member (Silurian of North-Eastern Saudi Arabia)[END_REF]. In both localities it is associated with graptolites of the ascensus and/or acuminatus zones (see discussion in Paris et al., this volume). The 3.5 ft thick highly bioturbated and condensed horizon yielding this assemblage is bracketed between the top of the Baq'a Sand

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Member of the Sarah Formation and a one foot thick bioturbated sandy bed at 253.5 ft corresponding to the first Aeronian deposits (see discussion in Melvin, this volume). A hiatus is interpreted to be present within the lowermost part of the Qusaiba Member at ca. 253.5 ft.

The Angochitina qusaibaensis interval-range Biozone

Definition. The definition of the qusaibaensis Biozone is slightly emended here. Originally, as defined by [START_REF] Paris | New chitinozoan species from Llandoverian subsurface strata of Saudi Arabia[END_REF], it corresponded to the interval-range biozone between the last occurrence (LAD) of Lagenochitina nuayyimensis directly overlain by typical Qusaiba shaly lithofacies (Fig. 3). The first sample available from

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these shales is 3.4 ft above the hiatus and yields an abundant and diverse chitinozoan assemblage typical of the qusaibaensis Biozone (Fig. 6). Most of the specimens of A.

qusaibaensis (25% to 36%) recorded in the lower part of the Qusaiba Member show a rather long neck (Plate I,5;Plate II,(6)(7)(8)(9) recalling those of A. hemeri. The chamber of A.

qusaibaensis has no true spines but the distinction between the two species may be difficult when the ornamentation is partly eroded. A peculiar structure, never previously reported, is visible on many specimens of A. qusaibaensis from the lower samples in the Qusaiba-1 well.

This unnamed structure consists of a very long membranous tubular sleeve (as long as the vesicle) extending from the prosome through the aperture (Plate II, 6a-b, 9 Plate II, 1-2). Among the subordinate species present are fairly rare but usually long ranging taxa occur (Fig. 6; Table 19), e.g. Pterochitina deichaii Taugourdeau, 1963 (Plate II, 3), Cutichitina minivelata sp. nov., Calpichitina sp. aff. C. densa (Eisenack, 1962), Conochitina vitrea Taugourdeau, 1962 andC. elongata (Plate I, 3-9). [START_REF] Paris | Final report on chitinozoans from well UDAYNAN. 1[END_REF][START_REF] Paris | Final report on the chitinozoans recorded in well TINAT[END_REF]. A last species is Conochitina viiuae sp. nov. a long slender species (Plate I, 2; Plate II, 4-5), abundant at 245.8 ft (15%; see Fig. 6).

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Range. In the Qusaiba-1 well, the qusaibaensis interval-biozone extends from 251.1 ft to 238.2/6 ft where the lowest occurring C. alargada are recorded (Fig. 6; Table 19). The base of the biozone is poorly defined in the NYYM-2 well (Paris et al., 1995, p. 81). Recent investigations on the chitinozoans of the Murzuk Basin, SW Libya [START_REF] Paris | Palynological and palynofacies analysis of early Silurian shales from the shallow borehole CDEG-2a in Dor el Gussa, eastern Murzuq Basin, Libya[END_REF] have shown that A. qusaibaensis is not associated with L. nuayyimensis at least in the main range part of the latter species. This is consistent with the range of A. qusaibaensis in UDYN-1,

where no specimens of L. nuayyimensis have been recorded [START_REF] Paris | New chitinozoan species from Llandoverian subsurface strata of Saudi Arabia[END_REF]. Because of the restricted range of M. olivieri sp. nov., identified as "Sphaerochitina sp. indet." in the upper investigated cores of wells TINT-2 (core 20, at 16.872 ft;[START_REF] Paris | Final report on the chitinozoans recorded in well TINAT[END_REF] and UDYM-1

(core 17 at 16.635.7 ft; [START_REF] Paris | Final report on chitinozoans from well UDAYNAN. 1[END_REF], it is considered that only the upper part of the qusaibaensis Biozone is represented in the Qusaiba-1 core hole.

Age assignment. In a previous paper, the base of the qusaibaensis Biozone was referred to the upper Rhuddanian, based on the occurrence of graptolites of the cyphus Biozone in its lowermost part in the TAYMA-1 well (see Paris et al., 1995, p. 81). The age of the upper part of the qusaibaensis Biozone, however, was not firmly constrained due to a sample gap at its highest occurrence in the NYYM-2 well, and to the absence of direct ties with graptolites or other fossils of stratigraphic value. The whole biozone was therefore tentatively referred to the upper Rhuddanian-lower Aeronian (Paris et al., 1995, fig. 4). The present material provides a much more precise calibration of the upper part of the qusaibaensis Biozone based on the graptolites of the convolutus Biozone recorded by [START_REF] Zalasiewicz | Early Silurian (Llandovery) graptolites from Central Saudi Arabia: first documented record of Telychian faunas from the Arabian Peninsula[END_REF] in the Qusaiba-1 core hole (Fig. 9). The interval attributed to the upper part of the qusaibaensis intervalbiozone (251.10 ft to 254.6 ft) yields graptolites of the convolutus Biozone, hence we can conclude that the qusaibaensis interval-biozone ranges from the upper Rhuddanian (upper part

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of the cyphus Biozone) to the mid-Aeronian (lower part of the convolutus Biozone). M. olivieri sp. nov. with a range apparently restricted to the upper part of the qusaibaensis Biozone, could represent a key chitinozoan species to indicate the early mid-Aeronian (i.e., lower part of the convolutus Biozone). It allows for instance to assign an early mid-Aeronian age for core 17 from the UDYN-1 well, and also for core 20 from the TINT-2 well.

Nevertheless, an olivieri subbiozone is not yet proposed as the FAD of M. olivieri sp. nov. is not completely documented (hiatus in the Qusaiba-1core hole; see above).

The Conochitina alargada total-range Biozone

Definition. This biozone is a close equivalent to the "Conochitina alargada -Plectochitina paraguayensis concurrent-range biozone" of [START_REF] Paris | New chitinozoan species from Llandoverian subsurface strata of Saudi Arabia[END_REF]. The closely spaced samples and the good graptolite control available in the Qusaiba-1 core hole, lead to a minor emendation of the original definition. The alargada Biozone is defined here as the total-range biozone of C. alargada [START_REF] Cramer | Chitinozoans of a composite section of Upper Llandoverian to basal Lower Gedinnian sediments in northern Leon, Spain[END_REF] In the Qusaiba-1 core hole, the base of this chitinozoan biozone is located 15.3 ft (ca. 4.6 m) above the base of the Qusaiba Member at 238.2/6 ft. The index species is moderately abundant in this sample (15% of the assemblage) but dominates the chitinozoan assemblage recorded at 235.4 ft (37%). C. alargada has its LAD at 210.9 ft with moderate to low abundances (Fig. 6). The top of the biozone is fixed at 210.9 ft in spite of the presence in this sample of very rare A. hemeri, the index species of the succeeding biozone (Figs. 6 and9). The alargada Biozone as defined here corresponds to "Assemblage 2" (="alargada-paraguayensis interval-range biozone") of [START_REF] Paris | Ranges and abundances of early Silurian chitinozoans in Qusaiba-1 shallow core (NE Saudi Arabia)[END_REF].

Main components.

The chitinozoan assemblages recorded in the alargada Biozone are diverse with up to 12 species (Fig. 6; Table 19). Angochitina qusaibaensis is the dominant

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species as it is the case in the underlying biozone (50% of the chitinozoans at 228.8 ft and 44% at 225.5 ft) (Fig. 6). ft. At the top of the biozone, at 210.9 ft, Plectochitina alnaimi sp. nov., a small form with birooted processes and blunt cones or granules on the chamber (Plate III,6), is abundant (23% at 210.9 ft) (Fig. 6; Table 19). This new species should be a useful guide for locating the top of the alargada Biozone.

Range. In the Qusaiba-1 core hole, the alargada interval-range biozone extends from 238.2/6 ft to 210.9 ft. The boundary with the overlying hemeri Biozone is not "sharp" as the first undisputable specimens of A. hemeri are observed at 210.9 ft, i.e. together with the last recorded C. alargada (Fig. 6; Table 19). In this sample A. hemeri is extremely rare (ca. 0.2% of the recorded chitinozoans) where A. qusaibaensis still represents 9% of all the chitinozoans recorded in this sample (see Fig. 6).

Age assignment. The graptolites of the convolutus Biozone identified by [START_REF] Zalasiewicz | Early Silurian (Llandovery) graptolites from Central Saudi Arabia: first documented record of Telychian faunas from the Arabian Peninsula[END_REF] in the Qusaiba-1 core hole provide a robust age control for the alargada Biozone as presently defined. The whole Qusaiba succession yielding chitinozoans of the alargada

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Biozone are unambiguously of mid-Aeronian age. This precise graptolite control also allows a mid Aeronian age to be assigned to some well-known, but previously poorly stratigraphically controlled species such as C. edjelensis, C. elongata, C. vitrea, P. deichaii and P.

pseudoagglutinans described by [START_REF] Taugourdeau | Association de Chitinozoaires dans quelques sondages de la région de Edjelé (Sahara)[END_REF]Taugourdeau ( , 1963) ) in south-eastern Algerian Sahara, Edjelé area, well Dl-101, samples at 2863 ft (871 m) and 2761 ft (840 m) depth. Similar assemblages occur also in Cyrenaica (eastern Libya) [START_REF] Molyneux | Palynostratigraphy of Northeast Libya[END_REF]Paris, 1988)

The Angochitina hemeri Biozone

Definition. This biozone is defined here as the interval-range biozone between the first significant (more than 3%) occurrence of A. hemeri and the FAD of A. macclurei [START_REF] Paris | New chitinozoan species from Llandoverian subsurface strata of Saudi Arabia[END_REF] It corresponds to the two former regional biozones defined by [START_REF] Paris | New chitinozoan species from Llandoverian subsurface strata of Saudi Arabia[END_REF] and respectively labelled "concurrent range biozone of Sphaerochitina solitudina and Angochitina hemeri" and "interval zone of A hemeri". These biostratigraphic subdivisions were defined from samples of cores 18 and 17 of the TINT-2 well, where an uncored interval of about 83 ft (25 m) separates the last occurrence of A. hemeri from the first occurrence of A.

macclurei. The material recovered from the Qusaiba-1 and Baq'a-4 core holes provides the missing information about this critical sample gap in the TINT-2 well and permits a much more accurate control on the base and on the top of the hemeri Biozone.

Main components.

In the Qusaiba-1 core hole, Angochitina species (Plate I,5;Plate II,(6)(7)(8) with the general morphology of A. hemeri (i.e., ovoid chamber with a long and slender neck) but with blunt spines or tubercles recalling the ornamentation of A. qusaibaensis are already present in the lowermost part of the Qusaiba Member. These puzzling specimens make it difficult to locate precisely the FAD of A. hemeri in the Qusaiba-1 core hole, where very rare

A C C E P T E D M A N U S C R I P T
(0.2%) specimens are recorded at 210.9 ft. Typical specimens of the index species from the sample at 176.05 ft are illustrated (Plate IV,(5)(6)Plate V,1). In the Baq'a-4 core hole A.

hemeri may be abundant (39 % of the identified individuals at 140.6 ft; Fig. 7; Table 20)

where it coexists with very rare C. alargada (Plate VIII,4), B. paravitrea (Plate VIII,5,8), and B. arabiensis (1% of the recorded species). Plectochitina alnaimi sp. nov. (Plate IV,9;Plate V,2,10), already present in the underlying biozone, is the most abundant species (from 17% at 167.7 ft to 70% at 140.1 ft) from the lower part of the hemeri Biozone in the Qusaiba-1 core hole (Fig. 6). It can be considered as an auxiliary species for identifying the lower part of the hemeri Biozone.

Other species are restricted to a single sample, where they can be abundant. Linochitina? sp.

(Plate VI, 1-2) is reported only in core 14 at 132.05 ft (29% of the recorded chitinozoans; Fig. 6). This form is kept in open nomenclature because the copula normally present in Linochitina species has not been observed (it might alternatively be referred to as an Euconochitina). [START_REF] Anthochitina | IGR 72288[END_REF] is exclusively recorded at 145.9 ft in the Qusaiba core hole. This species with a distinctive serrate or denticulate carina (Plate V,3,[START_REF]Three dimensional vesicle with the carina near the equator of the chamber and the small disc-like operculum[END_REF](12) represents 13% of the chitinozoans from this sample (Fig. 6). In the Baq'a-4 well, the most dominant species is Ancyrochitina gr. aculeata (up to 68% of the identified specimens).

Other species may be sporadically abundant in this well, such as C. caputoi (48% at 269.0 ft in the deepest investigated sample), or P. deichaii (13% at 269.0 ft) but discontinuously represented stratigraphically higher (Fig. 7; Table 20). Spinachitina geerti sp. nov. (Plate VII,1,(4)(5)(7)(8) is an interesting and fairly short ranging species, recorded only at 240.7 ft and 163.0 ft in Baq'a-4 (Fig. 7). Plectochitina paraguayensis Wood and Miller, 1991 (Plate IV, 7-8;Plate V, 5, 9) has its FAD at 240.35 ft (10%) in the Qusaiba-1 well and is moderately abundant (4 % to 18%) up to 145.9 ft. Plectochitina cf. clathrospinosa (Plate V,6) has very rare (less the 1%) and sporadic occurrences in the youngest samples of this Qusaiba-1 well

A C C E P T E D

M A N U S C R I P T (Fig. 6; Table 19). The isolated occurrence of very abundant Cyathochitina cf. caputoi (Plate IV, 1) at 167.7 ft is striking. This increase in abundance may be related to environmental changes more favourable for Cyathochitina species as e.g. Cyathochitina neolatipatagium sp.

nov. (Plate VI,(7)(8)[START_REF]Three dimensional vesicle with the carina near the equator of the chamber and the small disc-like operculum[END_REF] is also the dominant chitinozoan species (71% at 134.2 ft and 59% at 133.45 ft) in the upper part the Qusaiba-1 core hole (Fig. 6). [START_REF] Männil | Distribution of selected Ordovician chitinozoan assemblages and species in northern Europe and their stratigraphical evaluation[END_REF] Biozone in Baq'a-4 (Fig. 7), whereas the base of the succeeding macclurei Biozone is located at 140.6 ft in the Baq'a-4 core hole. In this well, indisputable A. macclurei specimens are associated with abundant representatives of A. hemeri at 140.6 ft. Consequently, the totalrange of these two biozonal index species overlaps slightly. In the Baq'a-4 well the hemeri Biozone extends in the Qusaiba Member, at least along a 106 ft (ca. 32 m) thick sequence from 269.0 ft to 163.0 ft, and possibly more, as there is an interval of 22.4 ft without available samples. The strata corresponding to the FAD of the index species were not penetrated in this well. In the TINT-2 well the biozone was documented in a 83 ft (25 m) thick interval. A.

hemeri (see synonymy in [START_REF] Paris | New chitinozoan species from Llandoverian subsurface strata of Saudi Arabia[END_REF] was originally called "Sphaerochitina longicollis form B" in [START_REF] Paris | Final report on the chitinozoans recorded in well TINAT[END_REF].

Age assignment. The hemeri Biozone was tentatively referred to the early Telychian by Paris et al. (1995) based on the known range of accompanying chitinozoan species in Baltoscandia [START_REF] Nestor | New Wenlockian species of Conochitina from Estonia[END_REF][START_REF] Nestor | Silurian chitinozoans[END_REF](Nestor, , 1994)), and recently calibrated by means of graptolites zones [START_REF] Loydell | Integrated biostratigraphy of the lower Silurian of the Aizpute-41 core, Latvia[END_REF][START_REF] Loydell | Integrated biostratigraphy of the lower Silurian of the Ohesaare core, Saarema, Estonia[END_REF][START_REF] Loydell | Integrated biostratigraphy of the lower Silurian of the Kolka-54 core, Latvia[END_REF]. In the present study numerous graptolites of the convolutus Biozone identified by [START_REF] Zalasiewicz | Early Silurian (Llandovery) graptolites from Central Saudi Arabia: first documented record of Telychian faunas from the Arabian Peninsula[END_REF] (restricted occurrence at 145.9 ft in the Qusaiba-1 core hole) was described by Nestor (1994, pl. VIII, figs. 1-6) from the uppermost part of the Velise Formation (sample at 140.1 m) in the Viki core hole, in Estonia. This sample was assigned to the lower part of the Adavere Baltic stage correlated with the turriculatus graptolite Biozone (see Nestor, 1994, fig. 28). A.

A C C E P T E D M A N U S C R I P T
primula is likely present in Québec, in the Jupiter Formation of similar age [START_REF] Achab | Biostratigraphie par les Chitinozoaires de l'Ordovicien Supérieur-Silurien inférieur de l'Ile de Anticosti[END_REF].

The Ancyrochitina camilleae subbiozone

Definition. This local subbiozone corresponds to the total-range of Ancyrochitina camilleae sp. nov. (Plate VIII,1,6) documented in the Baq'a-4 core hole (Fig. 7; A C C E P T E D M A N U S C R I P T

The Angochitina macclurei Biozone

Definition. This biozone as originally defined by [START_REF] Paris | New chitinozoan species from Llandoverian subsurface strata of Saudi Arabia[END_REF] corresponded to the acme-range biozone of Angochitina macclurei [START_REF] Paris | New chitinozoan species from Llandoverian subsurface strata of Saudi Arabia[END_REF] In its present usage, the macclurei Biozone corresponds to the interval-range biozone between the FAD of the index species and the LAD of Armoricochitina crassicarinata sp. nov. (Fig. 8; Table 21). This fits quite well with the total-range of A. macclurei. edjelensis (6% or less), P. pseudoagglutinans (Plate VII,6), and P. deichaii (Plate XVI,8), extend beyond the upper limit of the biozone as documented in the Baq'a-3 core hole (Fig. 8; saharica [START_REF] Taugourdeau | Association de Chitinozoaires dans quelques sondages de la région de Edjelé (Sahara)[END_REF] and P. combazii Cramer, 1967 because P. alisawyiahensis sp.

nov. has wider processes (see discussion below, in the Systematic section). The latter includes individuals with two (e.g., Plate IX,4,6;Plate XII,7) or several sets of simple /or branched processes anastomosed at their distal extremity (e.g., Plate XV,[4][5]8). P. alisawyiahensis is missing in some samples (e.g., in the lower part of the Baq'a-3 core hole) but dominates the neighbouring chitinozoan assemblage (55% of the taxa recorded at 450.1 ft) (Fig. 8; Table 21). The species extends above the FAD of A. macclurei and occurs sporadically up to 150.4

ft depth in the Baq'a-3 core hole.

Range. In Baq'a-4, the macclurei Biozone occurs from 140.6 ft to the highest investigated sample at 40.1 ft. Due to the sampling intervals, there is an uncertainty interval of less than 22.4 ft (6.8 m) on the FAD of the index species. In the Baq'a-3 core hole, A. macclurei occurs from the deepest processed sample at 518.3 ft up to 330.4 ft, i.e. in an interval of at least

A C C E P T E D M A N U S C R I P T
187.9 ft thick (ca. 57 m) (Figs. 8 and9). The last well-represented A. macclurei specimens are observed at 306.0 ft (Fig. 8; the specimen recorded at 250.5 ft is regarded as questionable).

Consequently, according to the definition adopted here the macclurei Biozone is very close to the total-range of the eponymous species. Moreover, A. macclurei is usually dominant in this biozone (relative abundances close to 50% or even exceeding 50% in the upper part of the biozone; see Fig. 8). This acme-interval was also documented in the TINT-2 well [START_REF] Paris | New chitinozoan species from Llandoverian subsurface strata of Saudi Arabia[END_REF], where the species was originally recorded under the .

Age assignment. The recent investigations on the graptolites from the Baq'a-3 and Baq'a-4 core holes [START_REF] Zalasiewicz | Early Silurian (Llandovery) graptolites from Central Saudi Arabia: first documented record of Telychian faunas from the Arabian Peninsula[END_REF] provide direct ties with the early Telychian guerichi and possibly turriculatus graptolite biozones (Fig. 9). The guerichi Biozone is documented in the Baq'a-4 well from 135.55 ft to 37.1 ft, and from 500.50 ft to 454.40 ft in the Baq'a-3 well, where the turriculatus Biozone sensu lato is identified at 367 ft and from 303 ft to 336 ft (Zalasiewicz et al., 2007, fig. 6). This means that the entire macclurei Biozone occurs within the lower Telychian. Until the recent investigations on the graptolites from the Qusaiba type area in northern Central Saudi Arabia, the macclurei Biozone was tentatively referred to the middle part of the Telychian (Paris et al., 1995, fig. 4). A. macclurei was restricted to the northern Gondwana regions and the previous correlation was therefore based on the range of accompanying species such as Calpichitina densa whose age assignment is better constrained in Baltoscandia [START_REF] Laufeld | Silurian Chitinozoa from Gotland[END_REF]Nestor, 1994). In spite of the compression that greatly modifies the silhouette of all the individuals available in the three studied core holes, the very distinctive chain-forming Desmochitininae from the Baq'a-4 (120.1 to 40.1 ft; see Fig. 7;

Table 20) and from the Baq'a-3 core holes (518.3 ft to 306.0 ft; Fig. (Hill et al., 1985, pl. 13, figs. 9a-b) or as M. margaritana (Paris, 1988a). C. densa, whose total range is virtually identical to that of A. macclurei in the Baq'a-4 and Baq'a-3 core holes, is a well-known species in the Telychian of Baltoscandia (see references in Nestor, 1994;[START_REF] Verniers | A global Chitinozoa biozonation for the Silurian[END_REF][START_REF] Loydell | Integrated biostratigraphy of the lower Silurian of the Ohesaare core, Saarema, Estonia[END_REF][START_REF] Loydell | Integrated biostratigraphy of the lower Silurian of the Kolka-54 core, Latvia[END_REF] and in the U.K. (see references in [START_REF] Mullins | Integrated Silurian chitinozoan and graptolite biostratigraphy in the Banwy River section[END_REF].

The Fungochitina merrelli subbiozone

Definition. This local subbiozone corresponds to the interval-range of Fungochitina merrelli sp. nov. between its FAD and the FAD of A. crassicarinata sp. nov., as documented in the Baq'a-3 and Baq'a-4 wells (Figs. [7][8]. and C. caputoi (Fig. 8; Table 21). Some other species, such as P. alisawyiahensis sp. nov.

(dominant species with a relative frequency of 55% at the base of the subbiozone), A. alhajrii sp. nov. (also well-represented in the biozone; Fig. 8) and C. densa, have their FAD close to, or at the base of the merrelli local subbiozone and extend above its upper limit. When compared to the abundance of A. alhajrii sp. nov. in the merrelli local subbiozone in the Baq'a-3 core hole (relative frequencies ranging from 42% in the uppermost merrelli subbiozone to 27% just above, at 388 ft), its absence in the Baq'a-4 well is puzzling. This absence of record may be due to the fact that only the lower part of the merrelli local subbiozone is documented in Baq'a-4. In that case the range of F. merrelli is much shorter in Baq'a-3 if one excludes the questionable individuals recorded at 518.3 ft in Baq'a-3.

Range.

In Baq'a-4, F. merrelli sp. nov. is recorded at 120.1 ft and at 40.1 ft (highest processed sample in this shallow core). Its total range is therefore present in at least of 80 ft (24.3 m) with an uncertainty of about 20.5 ft (6.2 m) concerning the FAD of the index species, due to the sample spacing (Fig. 7; Table 20). The absence of A. alhajrii sp. nov. and of A. crassicarinata sp. nov. in the highest investigated sample in the Baq'a-4 core hole, suggests that the top of the merrelli subbiozone is not reached at 40.1 ft in this shallow well (see discussion above).

In Baq'a-3, F. merrelli is recorded from 450.1 ft to 408.7 ft (in this last occurrence, however, its relative abundance is less than 1%). Thus, its total range is at least of 41.4 ft (12.6 m), with an uncertainty close to 20 ft, concerning respectively its FAD and its LAD, due to the sample spacing (Fig. 8; Table 21).

Age assignment. F. merrelli sp. nov. does not provide independent age control. Based on the

A C C E P T E D M A N U S C R I P T

associated graptolites of the guerichi Biozone recorded in wells Baq'a-4 (135.55 ft to 37.1 ft)

and Baq'a-3 (500.5 ft to 454 ft) (Zalasiewicz et al., 2007, figs. 6 and 5 respectively) the merrelli subbiozone fits almost perfectly within this lowermost Telychian graptolite biozone (Fig. 9).

The Armoricochitina crassicarinata subbiozone

Definition. This local subbiozone corresponds to the total range of Armoricochitina crassicarinata sp. nov., as documented in the Baq'a-3 core hole (Fig. 8; Table 21). A.

crassicarinata sp. nov. is a rather small chitinozoan (the vesicle length ranges around 120 µm). A. crassicarinata sp. nov. was reported in core 1 from well ISWH EW-9 with a provisional name Armoricochitina? sp. nov. A (see Paris, 1993, pl. 2: figs. 4-5).

Main components

Most of the species recorded in the macclurei Biozone, e.g. P. deichaii, C. densa, P.

alisawyiahensis sp. nov. with the exception of F. merrelli sp. nov. are represented in this subbiozone. Other taxa have their FAD within the crassicarinata subbiozone, e.g.

Tanuchitina obtusa (Plate XIII,(4)(5)Plate XVI,6;Plate XVIII,6) and representatives of the Ancyrochitina aculeata complex (Plate XII, 1; Plate XIII, 8; Plate XIV, 2). It must be noted that the lowest record of Cutichitina minivelata sp. nov. in the Baq'a-3 core hole does not represent the FAD of this species, which already occurs sporadically, but with higher relative abundances in older strata in the Qusaiba-1 core hole (Fig. 6; Table 19). Specimens

resembling Cingulochitina species at 350.1 ft (Plate XIII, 2) and at 330.4 ft are tentatively identified Armoricochitina? sp. (1% to 3 % of the recorded individuals) (Fig. 8; Table 21).

A C C E P T E D M A N U S C R I P T

Range. The crassicarinata local subbiozone is documented from 408.7 ft to 330.4 ft in the Baq'a-3, i.e. over 78.3 ft (ca. 24 m) of depth in the borehole (Fig. 8; Table 21). Due to the spacing of the samples, an interval of uncertainty of 23 ft (7 m) exists both for the FAD and LAD of A. crassicarinata and thus this subbiozone could range over at maximum of 125. Age assignment. A. crassicarinata is a new species and therefore, on itself, it does not provide an independent age control. Its location in the upper part of the macclurei regional Biozone supports an early Telychian age (see discussion above for the macclurei Biozone). At least the middle part of the crassicarinata subbiozone is tied to the turriculatus s.l. graptolite Biozone identified at 367 ft in the Baq'a-3 core hole (Zalasiewicz et al., 2007, fig. 5). Early

Telychian graptolites (turriculatus s.l. Biozone) are recorded in the upper part of the crassicarinata subbiozone at 336 ft in the Baq'a-3 core hole. It must be noted that no typical A. macclurei were recorded in well ISWH EW-9, and thus the uppermost range of A.

crassicarinata could extend slightly above the LAD of A. macclurei in this latter well.

The Tanuchitina obtusa Biozone

Definition. This regional biozone corresponds to the interval-range biozone between the LAD

A C C E P T E D M A N U S C R I P T

of Armoricochitina crassicarinata sp. nov. (i.e., equivalent to the FAD of Plectochitina jacquelineae sp. nov.) and the FAD of Euconochitina silurica (Taugourdeau, 1963). It must be noted that T. obtusa has its FAD within the upper part of the macclurei Biozone.

Considering the isolated record of a single specimen at 150.4 ft, the LAD of T. obtusa is within the succeeding silurica regional Biozone.

Main components. Tanuchitina obtusa [START_REF] Taugourdeau | Répartition et description des Chitinozoaires siluro-dévoniens de quelques sondages de la C.R.E.P.S., de la C.F.P.A. et de la S.N. Repal au Sahara[END_REF], the index species of this regional biozone, is a long chitinozoan (vesicle length ranging usually from 350 µm to 450 µm) with gently tapering straight flanks (Plate XIII,(4)(5)Plate XV,2;Plate XVI,6;Plate XVIII,6). It has sporadic occurrences and the recorded relative abundances do not exceed 10% (Fig. 8). Among the most common species is Plectochitina longicornis [START_REF] Taugourdeau | Répartition et description des Chitinozoaires siluro-dévoniens de quelques sondages de la C.R.E.P.S., de la C.F.P.A. et de la S.N. Repal au Sahara[END_REF]) (Plate XVI,7), which may represent up to 20% of the recorded species (Fig. 8; Table 21). This species has been previously reported from well ISWH EW-9 under the name P. paraguayensis "form B". It was recorded in cuttings from 3247 ft to 3594.9 ft (990 m to 1096 m), but not from core 1 at 3586.7 ft to 3601.4 ft (1093.5 m to 1098 m), so caving can be suspected for occurrence in the deeper cutting samples. In the discussion of P. paraguayensis Wood andMiller, 1991, Paris (1993) noted the great similarity between his "form B", P. longicornis and P. nodosa (the latter is herein regarded as a synonym of P. longicornis) but he did not assign this "form B" to P. longicornis for stratigraphical reasons. In Algeria, the type material of the two species was from cuttings located above an upper Silurian core sample. Recent investigations (F. Paris unpublished)

have not recorded P. longicornis or any morphologically similar forms in the late Silurian or in the Early Devonian of Algeria. Because a few sample mixing is proved in some of the older Saharan studies, a wrong location is also suspected for the type sample of P. longicornis, which may as well be of early Silurian age. In spite it is a nomen dubium the species name (the deepest records were possibly the result of caving). The striking occurrence of a large number (39% of the recorded chitinozoans at 206.9 ft; Fig. 8; Table 21) of Cyathochitina neolatipatagium sp. nov. in the upper part of the obtusa Biozone must be noted. A similar "bloom-like" event of this species was recorded in Qusaiba-1 within a short interval of less than 1.5 m thick in the upper part of the hemeri regional Biozone. Such bio-events are puzzling because they have no clear biostratigraphical explanation [START_REF] Männil | Distribution of selected Ordovician chitinozoan assemblages and species in northern Europe and their stratigraphical evaluation[END_REF]. They likely result from recurrent peculiar environmental conditions, which were specifically favourable for the Cyathochitina producers. A few C. neolatipatagium sp. nov. occur in core 1 of well ISWH EW-9 (not listed in [START_REF] Paris | Final report on chitinozoans from well ALISAWYIAH EW-9[END_REF].

A C C E P T E D M A N U S C R I P T
Range. The interval-range of T. obtusa extends for 99.1 ft depth (ca. 30 m) from 306.0 ft to 206.9 ft in the Baq'a-3 shallow core (Figs. [8][9]. Due to the sample spacing an interval of uncertainty respectively of ca. 20.3 ft and 14.4 ft (6.2 and 4.4 m) exists on the lower and upper limit of the biozone. In the ISWH EW-9 well, the obtusa Biozone occurs over 164 ft (ca. 50 m), and possibly more as the youngest cutting sample at 3254.1-3287 ft (990-1000 mstill contains A. gengi sp. nov. but not Euconochitina silurica, which is the index species of the succeeding biozone. In the ISWH EW-9 well, the obtusa Biozone as defined here corresponds to "Assemblages 3 and 4" of Paris (1993, fig. 2), whereas "Assemblages 1 and 2" correspond to the crassicarinata subbiozone in the terminal part of the macclurei regional biozone (Fig. 9).

Age

The Plectochitina jacquelineae sp. nov. subbiozone

Definition. This local subbiozone corresponds to the total range of Plectochitina jacquelineae sp. nov. The index species is only reported at 306.0 ft, in the sample yielding the last abundant A. macclurei. This is also the lowest available sample immediately above the top of the macclurei interval-range Biozone. In spite of the fact that it is restricted to a single sample

A C C E P T E D M A N U S C R I P T
in the Baq'a-3 core hole (Fig. 8; Table 21), this subbiozone is defined because Plectochitina jacquelineae sp. nov. has a distinctive morphology and is easy to identify, even on poorly preserved specimens (Plate XIV,4,6). caputoi (Fig. 8; Table 21).

Main components.

Range. During the present study, Plectochitina jacquelineae sp. nov. has been recorded only from a single sample at depth 306.0 ft in the Baq'a-3 core hole. Due to the spacing of the available samples, an uncertainty of ca. 23.1 ft (7 m) exists theoretically on its real LAD and FAD in Baq'a-3 (Fig. 8; Table 21). According to the synonymies proposed here, Plectochitina jacquelineae sp. nov. is also represented in the Qusaiba Member of the ISWH EW-9 well [START_REF] Paris | Final report on chitinozoans from well ALISAWYIAH EW-9[END_REF] and of the Tabuk and Qasim areas [START_REF] Mcclure | Chitinozoan and acritarch assemblages, stratigraphy and biogeography of the Early Palaeozoic of Northwest Arabia[END_REF].

Age assignment. Plectochitina jacquelineae sp. nov. is a new species, and thus cannot be used for independent dating of this subbiozone. In the Baq'a-3 core hole, however, Plectochitina jacquelineae sp. nov. occurs with graptolites of the turriculatus s. l. Biozone indicating an early Telychian age for this subbiozone. A similar age is proposed for the corresponding strata in the ISWH EW-9 well.

Fairly closely related forms, such as Anthochitina primula Nestor, 1994, or individuals identified as Ancyrochitina ansarviensis Laufeld (in Nestor, 1994, pl. 1, fig. 7) are known in

A C C E P T E D M A N U S C R I P T
the Adavere regional stage in the Baltic area, i.e., in the upper Telychian according to the correlation proposed by Nestor (1994) and improved by comparisons between graptolites and chitinozoan biozonations [START_REF] Loydell | Integrated biostratigraphy of the lower Silurian of the Aizpute-41 core, Latvia[END_REF][START_REF] Loydell | Integrated biostratigraphy of the lower Silurian of the Ohesaare core, Saarema, Estonia[END_REF][START_REF] Loydell | Integrated biostratigraphy of the lower Silurian of the Kolka-54 core, Latvia[END_REF].

The Plectochitina lucasi sp. nov. subbiozone

Definition. The subbiozone corresponds to the total range biozone of Plectochitina lucasi sp.

nov. The index species (Plate XV,3,7) is the dominant species in the lower part of the obtusa Biozone (e.g., 63% of the recorded individuals at 271.8 ft; see Fig. 8). This new species (see Systematic section) has a distinctive silhouette. The processes are hollow and display lambda or multi-rooted proximal ends (Plate XV,7b). This new species was reported in well ISWH EW-9 in open nomenclature as "Ancyrochitina n. sp. B" (see [START_REF] Paris | Final report on chitinozoans from well ALISAWYIAH EW-9[END_REF]pl. 2, figs. 1-2).

Main components. The accompanying species are the long ranging P. deichaii, and shorter ranging species, e.g. Plectochitina alisawyiahensis sp. nov., C. minivelata sp. nov., A. gr.

aculeata, and T. obtusa (see Fig. 8 and description of the obtusa Biozone above).

Range. P. lucasi sp. nov. occurs from 289.1 ft to 250.5 ft, i.e. at least over 38.6 ft (11.7 m).

Due to the sample spacing, an interval of uncertainty of respectively 16.9 ft (5.15 m) and 20.8 ft (6.3 m) exists for the base and the top of the lucasi subbiozone in the Baq'a-3 shallow core (Fig. 8; Table 21).

If one accepts the synonymy proposed here between P. lucasi sp. nov. and "Ancyrochitina n.

sp. B" in [START_REF] Paris | Final report on chitinozoans from well ALISAWYIAH EW-9[END_REF], it ranges in the ISWH EW-9 well in cuttings samples from 3470.2 ft to 3588.3 ft (1058 to 1094 m). Thus, it range is over 118 ft (36 m; see Fig. 9), and likely less

A C C E P T E D M A N U S C R I P T
because the deepest individuals could be caved, as they occur within the upper range of A. crassicarinata in "Assemblage 2" of [START_REF] Paris | Final report on chitinozoans from well ALISAWYIAH EW-9[END_REF]. The absence of P. lucasi sp. nov. in core 1 (1993.5 to 1098 m) in the ISWH EW-9 well confirms this interpretation.

Age assignment.

No graptolites are recorded in the samples yielding P. lucasi sp. nov.

Moreover, the chitinozoan species recorded in the lucasi subbiozone do not allow direct correlation with the early Silurian chronostratigraphy. Thus the same arguments as for the obtusa Biozone are used for determining the age of the lucasi subbiozone. The absence of Margachitina margaritana, a widespread early Sheinwoodian chitinozoan, is regarded as an argument for keeping the lucasi subbiozone in the Telychian.

The Euconochitina silurica Biozone

Definition. This biozone corresponds to the total range biozone of Euconochitina silurica (Taugourdeau, 1963). The LAD of the index species is not documented in the processed material (no sample available above 130 ft in the Baq'a-3 core hole). Taugourdeau (1963) defined E. silurica in a core sample from the eastern part of the Illizi Basin, SE Algerian Sahara (sample at 1445 m depth in well Zr. 1). The original name was Conochitina oelandica subsp. silurica. This subspecies is raised here to species rank because of its discriminating characters. E. silurica is a very small chitinozoan (Plate XVIII,(3)(4), which has a total length ranging around 90-110 µm in the investigated samples. It displays a conical chamber with a rounded margin. The sub-cylindrical neck may represent half to one third of the vesicle length. The vesicle wall is smooth; a small scar occurs on the apex of the vesicle (Plate XVIII,4).

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Main components. Several taxa present in the underlying biozones range into this biozone (Fig. 8; Table 21). They include the highest occurring specimens of P. deichaii, as well as representatives of P. alisawyiahensis sp. nov. The latter may be fairly abundant (e.g., 18% of the recorded specimens at 150.4 ft), Calpichitina cf. acollaris (Plate XVII,6,8) and C. minivelata sp. nov., which has a surprisingly high relative frequency (62%) at 192.5 ft, when E silurica has its FAD (Fig. 8; Table 21). Other species range into the silurica Biozone.

Armoricochitina gengi sp. nov. (Plate XVII, 1-2) dominates the assemblage (42% of the recorded individuals) at 150.4 ft, whereas another form, tentatively identified as Fungochitina? sp. (Plate XVII,(3)(4)(5), is the most abundant form (51%) at 170.9 ft (Fig. 8;

Table 21). Fungochitina? sp. has a fungiform chamber, which may be variously modified during lateral compression of the vesicle (e.g., Plate XVII,4). The walls bear granules to small spines. The most striking element, however, is the very short and irregular rim-like structure (remains of a carina?) running around its rounded margin. To some extent, such structure recalls the short carina of

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Range. The silurica regional Biozone occurs from 192.5 to 130.0 ft, in the upper 62.5 ft (19 m) of the Baq'a-3 core hole. This interval thickness must be regarded as a minimum as the relative abundance of the index species is very high in the last processed sample and the biozone most likely extends into younger strata not investigated here. The stratigraphic range of the index species is unknown in its type locality in Algeria, which is based on an isolated sample.

Age assignment. The silurica regional Biozone, like the preceding ones, does not contain chitinozoan species permitting an independent age assignment. Again, the absence of Margachitina margaritana, which has a FAD that is well-constrained in British sections [START_REF] Mullins | Integrated Silurian chitinozoan and graptolite biostratigraphy in the Banwy River section[END_REF] and in Baltoscandian sections (Nestor, 1994;[START_REF] Loydell | Integrated biostratigraphy of the lower Silurian of the Ohesaare core, Saarema, Estonia[END_REF][START_REF] Loydell | Integrated biostratigraphy of the lower Silurian of the Kolka-54 core, Latvia[END_REF], is used here for tentatively dating the silurica Biozone as pre-Sheinwoodian. No graptolite remains have been observed from the samples yielding E. silurica. This may result from too shallow-water environments in the uppermost part of the Qusaiba Member as indicated by the abundance of eurypterid remains in the organic residue (Silurian eurypterids are usually regarded as near-shore organisms). The occurrence of retiolitid graptolites just below the base of the silurica Biozone is compatible with a late Telychian age for this biozone (possibly within the time interval corresponding to the spiralis to centrifugus graptolite zones). The silurica Biozone is here regarded as a faunal indicator of the upper part of the Qusaiba Member, close to its boundary with the Sharawra Member.

Chronostratigraphy of the Qusaiba Member

One informal assemblage ("Assemblage 1" in Paris et al., this volume) and six chitinozoan

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biozones have been identified in the investigated samples from the Qusaiba-1, Baq'a-4 and Baq'a-3 core holes. In ascending order are the qusaibaensis (pro parte), alargada, hemeri, macclurei, obtusa and silurica biozones. These biozones are considered of regional value, i.e. Whenever the sedimentary record is complete, the qusaibaensis interval-range Biozone originates in the upper Rhuddanian and ends in the early mid-Aeronian. In the Qusaiba-1

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shallow core, only the upper part of the qusaibaensis Biozone corresponding to the convolutus graptolite Biozone pro parte [START_REF] Zalasiewicz | Early Silurian (Llandovery) graptolites from Central Saudi Arabia: first documented record of Telychian faunas from the Arabian Peninsula[END_REF] is represented in cores 27 (upper part)

and 26. This upper part of the qusaibaensis is well characterized by Muscochitina olivieri sp.

nov. a taxon also recovered in core 20 in the TINT-2 well and in core 17 of the UDYN-1 well.

In the Qusaiba-1 core hole, the alargada interval-range Biozone reported from cores 25 to 22 is assigned to the middle Aeronian, based on the combined occurrence of the chitinozoans with graptolites of the lower part of the convolutus Biozone (Fig. 9).

The hemeri interval-range Biozone is documented in the upper part of the Qusaiba-1 and in the lower part of the Baq'a-4 core holes [START_REF] Paris | Ranges and abundances of early Silurian chitinozoans in Qusaiba-1 shallow core (NE Saudi Arabia)[END_REF][START_REF] Paris | High resolution biostratigraphy of early Silurian chitinozoans in Baq'a-3 and no. 4 shallow cores (NE Saudi Arabia)[END_REF]. This biozone was identified also in deep core samples from eastern Central Saudi Arabia [START_REF] Paris | New chitinozoan species from Llandoverian subsurface strata of Saudi Arabia[END_REF], e.g. core 17 from UDYN-1 [START_REF] Paris | Final report on chitinozoans from well UDAYNAN. 1[END_REF] and cores 17-20 from TINT-2 [START_REF] Paris | Final report on the chitinozoans recorded in well TINAT[END_REF]. Graptolites of the convolutus Biozone are associated with the chitinozoans of the hemeri Biozone, both in the Qusaiba-1 (cores 22 to 14) and in the Baq'a-4 (cores 31 to 19) wells. These graptolites provide a precise correlation with the middle part of the Aeronian [START_REF] Zalasiewicz | Early Silurian (Llandovery) graptolites from Central Saudi Arabia: first documented record of Telychian faunas from the Arabian Peninsula[END_REF].

The camilleae sp. nov. total-range subbiozone is identified in the upper part of the hemeri Biozone, cores 23 to 19 (i.e., middle part of the Baq'a-4 core hole). The mid-Aeronian age assignment of the camilleae subbiozone is based on its direct calibration by graptolites of the convolutus Biozone (Fig. 9).

The macclurei interval-range biozone is identified in the upper part of the Baq'a-4 and in the lower part of the Baq'a-3 shallow cores. The early Telychian graptolites [START_REF] Zalasiewicz | Early Silurian (Llandovery) graptolites from Central Saudi Arabia: first documented record of Telychian faunas from the Arabian Peninsula[END_REF] occurring with the index species in the two shallow cores provide a precise and independent calibration of this biozone. Its lower part is represented in cores 17 to 7 (i.e. from Biozone in core 40 (367 ft), and in cores 34 and 36 of early Telychian age (Fig. 9). The macclurei Biozone was originally defined in core 16 of TINT-2 well and tentatively attributed to the late Telychian [START_REF] Paris | New chitinozoan species from Llandoverian subsurface strata of Saudi Arabia[END_REF]. The present data indicate that this previous dating must be corrected. The macclurei Biozone range is restricted to the lower Telychian.

The merrelli sp. nov. total-range subbiozone is identified in cores 15 to 7 from the uppermost part of the Baq'a-4 well and from cores 49 and 47 from the lower part of the Baq'a-3 well.

This subbiozone, which represents the lower part of the macclurei Biozone, has been documented in other Saudi Arabian wells. It is assigned to the early Telychian as it is bracketed by graptolites of the guerichi and turriculatus biozones (Fig. 9).

The crassicarinata sp. nov. total-range subbiozone is identified in cores 45 to 36 (from 408.7 ft to 330.4 ft) from the middle part of the Baq'a-3 core hole. This subbiozone is wellrepresented the ISWH EW-9 well (core 1, and cuttings corresponding to "Assemblage 2" in [START_REF] Paris | Final report on chitinozoans from well ALISAWYIAH EW-9[END_REF]. The subbiozone is most likely present in the upper part of core 16 from the TINT-2 well after a reappraisal of the less well-preserved individuals, unnamed in Paris (1992). The crassicarinata subbiozone is assigned to the early Telychian based on a direct graptolite calibration in the Baq'a-3 core hole where the crassicarinata subbiozone occurs with graptolites (M. e.g. gr. marri at 367 ft and S. becki at 336 ft). Zalasiewicz et al. (2007, fig. 5) referred these graptolites to the turriculatus s.l. Biozone (Fig. 9).

The obtusa interval-range Biozone is identified in the upper part of the Baq'a-3 well (cores 34 to 22, i.e. from 306.0 ft to 206.9 ft), and in core 1 and cuttings samples from 3293. [START_REF] Zalasiewicz | Early Silurian (Llandovery) graptolites from Central Saudi Arabia: first documented record of Telychian faunas from the Arabian Peninsula[END_REF] the subbiozone also can be attributed to the lower Telychian. Core 34 from the Baq'a-3 well and the cuttings from the ISWH EW-9 are therefore tentatively assigned to the lower Telychian.

The lucasi sp. nov. total-range subbiozone occurs from core 32 to core 27 (from 289.1 ft to 229.7 ft) in the middle part of Baq'a-3. The lucasi subbiozone is also documented in ISWH EW-9 well where the index species occurs in "Assemblage 3" sensu [START_REF] Paris | Final report on chitinozoans from well ALISAWYIAH EW-9[END_REF] in cuttings from 3470.5 ft to 3509.6 ft (1058 to 1070 m). In the ISWH EW-9 well the specimens recorded below in the borehole are possibly caved. The lucasi subbiozone is tentatively attributed to the middle and/or upper Telychian as it occurs just above samples yielding graptolites of the turriculatus s.l. Biozone (Fig. 9).

The silurica total range Biozone is identified in cores 21 to 14 from the uppermost part (192.5 ft to 130.0 ft) of the Baq'a-3 well. Its upper part is not documented in this shallow core (no samples processed above core 14). The silurica Biozone is known in other northern

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Gondwana regions, e.g. in SE Algeria. The shallow environments of the Sharawra Member, which extends above core 14 in the Baq'a-3 well, seem unfavourable for graptolites.

Therefore, this fossil group will be of no help for dating the upper part of the silurica Biozone. This biozone is tentatively attributed to the late Telychian (Fig. 9) because no typical early Sheinwoodian chitinozoans, known to occur elsewhere in the Sharawra Member (Al-Hajri and [START_REF] Al-Hajri | Age and palaeoenvironment of the Sharawra Member (Silurian of North-Eastern Saudi Arabia)[END_REF], are observed in this biozone.

Qusaiba environments and chitinozoan taphonomy

The abundance of the recorded chitinozoans in each sample of the three investigated wells has been collated with the lithology of the processed material (Tables 123 of rock). In the latter well, the most evident trend is an increase in the chitinozoan abundances through time, independently of the colour of the sediment. This high chitinozoan production drops significantly in the uppermost part of the well (core 14), in more silty deposits (at 133.45 ft) or deposits with sandy laminae (132.05 ft). In this core hole, eurypterid fragments occur exclusively in these two samples and a temporary shallowing is interpreted. A similar, but more conspicuous and sustained trend is also recorded in the upper part of the Baq'a-3 core hole. In this well, a correlation between a lowering of the chitinozoan abundances and the occurrence of eurypterid remains is also noticed (Table 3). A shallowing trend announcing the nearshore environments of the overlying Sharawra Member is registered in the upper part of this core hole, particularly in core 14 with the grey siltstone and sandy laminae at 130.0 ft.

This sample has by far the lowest chitinozoan abundance (27 specimens per gram of rock)

among the processed samples in the three investigated core holes.

To summarize, the chitinozoan abundances do not exactly reflect the lithology, as shale or siltstone samples can yield more than 9000 chitinozoans per gram of rock but conversely these two types of sediment may contain less than 100 chitinozoans per gram of rock. The most obvious limiting factor for the proliferation of most of the chitinozoan species seems to be the shallow water depositional environments. On the contrary for some species such as C. neolatipatagium sp. nov., these environments seem to be the most suitable (see below). The highest abundances (exceeding 9000 chitinozoans per gram of rock Table 1) are in environments leading to condensed sequences (see Melvin, this volume), e.g. the highly bioturbated carbonaceous dark shale at 254.8 ft in the Qusaiba-1 core hole (see Melvin, this volume).

Independently of the recorded chitinozoan abundances, slight discrepancies are noted in the

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detailed range of some species within the Saudi Arabian Silurian sequences (Figs. [6][7][8]. They may be partly related to sporadic occurrences and/or to the spacing of the samples. Most of these discrepancies, however, result from an environmental control on the distribution of peculiar chitinozoan species. Several taxa such as Plectochitina alisawyiahensis sp. nov. seem to be better represented in fine-grained deposits (see Table 3 andFig -8). Species such as Cyathochitina neolatipatagium sp. nov. (at 206.9 ft in the Baq'a-3 and in core 14 in Qusaiba-1 core holes) or even Cyathochitina caputoi have more intermittent occurrences recalling the distribution of opportunistic taxa, with bloom-like occurrences (i.e., sudden and brief proliferation, with a "Lazarus" distribution). The temporary absence of specific predators may also explain the sudden proliferation of some chitinozoan species (see discussion in [START_REF] Grahn | Emergence, biodiversification and extinction of the chitinozoan group[END_REF]. C. neolatipatagium sp. nov. seems dependent on the more shallow siltier environments in Qusaiba-1 (see Table 1 and Fig. 6) and Baq'a-3 (Table 3, Fig. 8).

Consequently, when selecting the index species of biozones (or subbiozones) and when proposing correlation between different sections or wells, we have paid much attention to examine how far the acme biozone of a species reflects the optimal development of a species

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or results from a "bloom-like" proliferation driven by local optimal environmental conditions.

Conclusions

The chitinozoan assemblages recovered from the Qusaiba Member of the Qalibah Formation The shallowing trend preceding the more nearshore environments of the Sharawra Member is registered by a decrease in diversity and abundance of the chitinozoans, but also by an increase in the eurypterid remains within the organic residue.

The investigations carried out on the Qusaiba Member have revealed a biodiversity of the chitinozoans through time much higher than documented previously. This allowed to describe numerous new species in the present paper. It is clear that the former published studies missed some important intervals. This was mainly due to a discontinuous and too scattered sampling of the Qusaiba sequence. One can expect now chitinozoan correlation at the scale of the Arabian palaeoplate with accuracy close to or in a few cases even more detailed than that of graptolites from this Qusaiba Member. For a long time the Saudi Arabian chitinozoan biozones suffered of a deficit of precise calibration with regard to the Silurian standard chronostratigraphy. The present study contributes significantly to improvement of the available dating in terms of Llandovery stages, thanks to the excellent ties provided by the graptolites coexisting with the chitinozoans in the upper part of the Qusaiba Member. This study indicates also that a single section is not sufficient for elaborating a regional biostratigraphic model when the geological context (major rapid transgression, or glaciation) is susceptible to generate condensed sequences or gaps of various magnitudes.

Appendix A. Main lithological and palaeontological data concerning the processed samples (Tables 123)

Subfamily Conochitininae [START_REF] Paris | Les chitinozoaires dans le Paléozoïque du sud-ouest de l'Europe (Cadre géologique -Etude systématique -Biostratigraphie)[END_REF] Genus Conochitina [START_REF] Eisenack | Neue Mikrofossilien des baltischen Silurs I[END_REF] The resulting differential flattening simulates a constriction in the middle part of the vesicle (Plate II,(4)(5). The walls are perfectly smooth and rather thick, particularly near the margin (holotype not compressed, and thus no coefficient of correction used on Table 4). The bottom of the chamber is convex or has a truncated ogival profile due to the presence of a large circular mucron with a flat top (Plate II,4b). The diameter of this mucron is close to half the diameter of the chamber.

Measurements (Table 4; Figs. 10a-b). A few less typical individuals are reported at 251.1 ft (Plate I, 2) and at 238.2 ft in the same well (Fig. 6; Table 19). These strata belong to the upper part of the qusaibaensis Biozone, which is assigned to the mid-Aeronian, based on the independent age control provided by graptolites of the convolutus Biozone [START_REF] Zalasiewicz | Early Silurian (Llandovery) graptolites from Central Saudi Arabia: first documented record of Telychian faunas from the Arabian Peninsula[END_REF]. This new species is likely rare and has a short range as it has not been reported yet in other subsurface chitinozoan assemblages from the Qusaiba Member. In all likelihood, the species is present (see synonymy) in a core sample from well D1-31 in Cyrenaica, eastern Libya [START_REF] Molyneux | Palynostratigraphy of Northeast Libya[END_REF]Paris, 1988a).

Subfamily Spinachitininae [START_REF] Paris | Les chitinozoaires dans le Paléozoïque du sud-ouest de l'Europe (Cadre géologique -Etude systématique -Biostratigraphie)[END_REF] Genus Spinachitina [START_REF] Schallreuter | Neue Chitinozoen aus ordovizischen Geschieben und Bemerkungen zur Gattung Illichitina[END_REF] Diagnosis: Large Spinachitina species with a conical chamber prolonged by a neck flaring near its fringed aperture; crown of well developed spines on the margin; randomly distributed robust spines on the chamber and on the neck; this ornamentation decreases on the chamber bottom and on the neck.

Description:

The total length of this quite long chitinozoan (mean length: 252 µm; length of the holotype: 231 µm) shows important variations (see Table 5; Figs. 11a-b) with L ranging from 322 µm (Plate VII,4) to 141 µm (Plate VII, 5; the latter, however is possibly broken or teratological). The general silhouette of the vesicle is rather variable, with a fairly constant chamber width but a highly variable length due principally to the development of the neck.

There is a positive correlation between the vesicle length (L) and the chamber length (lp) (Fig.

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11b). Some elongate specimens have a long tubular neck ending with a flaring collarette. The aperture is serrated (Plate VII,7a). The flanks taper progressively up to the base of the neck, which is separated from the chamber by a poorly differentiated shoulder and by a weak flexure (Plate VII,1,4). A slight constriction occurs in the third lower part of the chamber. A sharp margin corresponding to the maximum diameter of the chamber separates a slightly convex bottom from the flanks. The convexity of the anti-apertural end is accentuated by the folding downwards of the chamber bottom during compression (e.g. Plate VII,7b). This fold usually obscures the apex of the vesicle and thus the antiapertural structure is not welldocumented. A large flat circular area surrounded by a low rim is present (Plate VII, 1). The main discriminating characters of this species are the combination of the crown of fairly long spines running along the margin, and the robust and well-developed spines on the chamber (Plate VII,1,7b,8). The spiny crown is composed of ca. 30 quite long tapering spines (length up to 12 µm), densely and regularly distributed along the margin (Plate VII, 7b, 8) and directed anti-aperturalwards. Robust but shorter conical spines are randomly distributed on the chamber (Plate VII,7b,8). This spiny ornamentation fades away toward the neck where they are reduced to granules or to blunt cones. The chamber bottom below the crown surrounding the margin is smooth (Plate VII, 1) or carries small granules (Plate VII,7b,8).

Measurements (Table 5; Figs. 11a-b). Van [START_REF] Van Grootel | Litho-en Biostratigrafische studie met Chitinozoa in het westelijk deel van het Massief van Brabant[END_REF] show the same important variations of the vesicle length (L) ranging from 140 to 333 µm (mean: 226 µm) for the Belgian population (see Table 5, for comparison).

Because the occurrence of a spiny ornamentation on its flanks, Spinachitina geerti sp. nov.

clearly differentiates from the other early Silurian Spinachitina species, especially from S.

fragilis (Nestor, 1980a), which has a similar silhouette (e.g., see Bourahrouh, 2002;[START_REF] Butcher | Early Llandovery chitinozoans from Jordan[END_REF]. S. maennili (Nestor, 1980b) has a sub-cylindrical vesicle and no ornamentation on the chamber. A few Late Ordovician species have spiny walls such as S. cervicornis [START_REF] Eisenack | Neue Mikrofossilien des baltischen Silurs I[END_REF] and S. taugourdeaui [START_REF] Eisenack | Microfossilien eines Geschiebes der Borkholmer Stufe, baltisches Ordovicium, F2. Mitt[END_REF]). These two species, however, have more strongly developed processes on their margin. S. imperita [START_REF] Dicevitchius | Some new species of Chitinozoa from Ordovician and Silurian deposits of the south Baltic and of northwestern Byelorussia. 1. Acanthochitina and some Conochitina[END_REF]) has a different silhouette as its cylindrical neck is longer than the chamber. Moreover, its wall seems

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glabrous.

During previous investigation on the subsurface chitinozoans from Saudi Arabia, rare Spinachitina specimens with a spiny ornamentation on the chamber have been recorded in cores 18 to 20 of the UDYN-1 well. Some of the recovered specimens with subcylindrical vesicles were tentatively referred to S. sp. aff. maennili by [START_REF] Paris | Final report on chitinozoans from well UDAYNAN. 1[END_REF]. Other ones with less obvious spines on the chamber were assigned to S. maennili (Nestor, 1980b) In Saudi Arabia, if one accepts the synonymy proposed here, S. geerti sp. nov. ranges through the Aeronian as documented in the UDYN-1 and Baq'a-4 wells. However, its relative abundance is very low in the early Aeronian. A specimen recorded in core 19 (160.3 ft) in the Baq'a-4 well displays a crown of numerous (ca. 50) short blunt spines on the margin and bears tubercles on its flanks (Plate VIII,2). It is provisionally referred to S. geerti sp. nov. as

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it may correspond to a corroded specimen. If the suggested synonymy of the specimens recorded by [START_REF] Al-Hajri | Systematics and biostratigraphy of Middle Ordovician to Lower Silurian chitinozoans of the Arabian Peninsula[END_REF] in the "QA" well is confirmed by SEM observations, the species is also present in the Qusaiba Member in the subsurface of the Tabuk area (northern Saudi Arabia).

Family Lagenochitinidae [START_REF] Eisenack | Neue Mikrofossilien des baltischen Silurs I[END_REF], emend Paris, 1981 Subfamily Cyathochitininae [START_REF] Paris | Les chitinozoaires dans le Paléozoïque du sud-ouest de l'Europe (Cadre géologique -Etude systématique -Biostratigraphie)[END_REF] Genus Cyathochitina Eisenack, 1955b, emend Paris et al., 1999 Type species: Conochitina campanulaeformis [START_REF] Eisenack | Neue Mikrofossilien des baltischen Silurs I[END_REF] Cyathochitina neolatipatagium sp. nov. Paris (Plate VI,(7)(8)[START_REF]Three dimensional vesicle with the carina near the equator of the chamber and the small disc-like operculum[END_REF] 1988 -Cyathochitina campanulaeformis [START_REF] Eisenack | Neue Mikrofossilien des baltischen Silurs I[END_REF]

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Type locality: Qusaiba-1 core hole, core 14, North Central Saudi Arabia.

Type stratum: Qusaiba Member of the Qalibah Formation, core 14, 135.5 ft, mid-Aeronian (hemeri Biozone).

Paratypes: Plate VI, 7, core 14, at 133.45 ft, IGR 72298, (Q50); Plate VI, 11, core 14, at 136.5 ft, IGR 72293, (Q40).

Material: 1585 specimens picked from the organic residues of core 14 (4 samples, see Fig. 6) from the Qusaiba-1 core hole. Some of the sorted specimens were used for  13 C chit. analyses and for chemical organic analyses of the chitinozoan wall [START_REF] Jacob | New insights into the chemical composition of the chitinozoans[END_REF]; 114 specimens picked in cores 25 and 22 from the Baq'a-3 core hole (Fig. 8; Table 21).

Diagnosis: Large Cyathochitina species with a short cylindrical neck, a thickset conical chamber, and a very wide and rather thick carina extending perpendicularly from a thickwalled margin; the glabrous chamber has a corrugate surface; concentric rim pattern occurs on the carina.

Description: This Cyathochitina species is quite large with the diameter of the chamber (excluding the carina) ranging from 117 to ca. 240 µm (mean diameter: 168 µm) (see Table 6;

Fig. 12). The holotype is partially compressed along its longitudinal axis. Consequently, the actual lengths of the vesicle and neck are likely higher than the measures reported on Table 6.

This vertical compression is due to its wide diameter (maximum diameter of the vesicle, including the carina = 227 µm) exceeding the vesicle length and to the thickened margin that prevent the lateral flattening (the vesicle settles on its bottom, instead of on its flanks as is the rule for elongated vesicles). Such oriented deformation is frequently observed in the examined populations (Plate VI,(7)(8). The neck is cylindrical and its length does not exceed the length of the thickset chamber. The flanks are normally straight (no shoulder) and taper rapidly toward the conspicuous flexure. The widened lower part of the chamber of the paratype (Plate VI, 7) is due to the differential compression of the flanks and of the occurrence of a thickened

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margin. The vesicle surface is glabrous, but variably developed corrugations are visible on the chamber wall. This pattern results from cross distribution of low longitudinal and horizontal elevations (or of discrete thickenings of the wall). The carina is well-developed (mean width: 22.7 µm; see Table 6) and displays concentric thickened rims or ridges (visible mainly in transmitted light microscope). This double-walled carina, with a rounded border (Plate VI,7) is oriented perpendicular to the margin. Its width is variable (ranging from 10 to 44 µm) and seems generally correlated with the chamber diameter (Fig. 12). Nestor (1994) illustrated individuals identified as Cyathochitia kuckersiana [START_REF] Eisenack | Neue Mikrofossilien des baltischen Silurs III und neue Mikrofossilien des bohmischen Silurs[END_REF] from the Varkla core in Estonia. One of the specimens recorded by this author (pl. XXIII, fig.

8) in strata from the Raikülla regional stage (Aeronian) shows the circular rims and the rounded edge of C. neolatipatagium sp. nov. In our opinion, this justifies the synonymy proposed here, even if Nestor (1994, p. 80) considers the Late Ordovician and the early Silurian Cyathochitina with a morphology recalling C. kuckersiana as probable intraspecific variations of this species.

Range and geographic distribution:

The new species is extremely abundant (up to 70% of the recorded specimens; see Fig. 6; Table 19) in the upper part (cores 14 to 16) of the Qusaiba-1 core hole. The corresponding strata represent part of the Qusaiba Member of the Qalibah Formation, assigned to the mid-Aeronian based on an independent graptolite control [START_REF] Zalasiewicz | Early Silurian (Llandovery) graptolites from Central Saudi Arabia: first documented record of Telychian faunas from the Arabian Peninsula[END_REF]. C. neolatipatagium sp. nov. occurs also in the Baq'a-3 core hole where it is the dominant species in core 22 at 206.9 ft (39% of the identified chitinozoans; Fig. 8). In core 25, at 229.7 ft, it represents only 1%, but in a much more abundant assemblage. In the Baq'a-3 well the corresponding samples are still from the Qusaiba Member, but they are referred to the upper part of the obtusa Biozone, which is tentatively assigned to the mid-Telychian (see discussion above, and Fig. 9). The distribution of C. neolatipatagium sp. nov. in the Qusaiba Member is striking. It seems to be controlled by sporadic "blooms", by environmental changes (e.g., more silty facies; see Table 1 and3) or by variations in their predation. C. neolatipatagium sp. nov. is only reported from Saudi Arabia.

If one accepts the proposed synonymy, this new species occurs also in the Qusaiba Member of the Qalibah Formation of the Qasim and Tabuk areas in Saudi Arabia, and in the Aeronian of Estonia (Varkla core; see Nestor, 1994).

Subfamily Ancyrochitininae [START_REF] Paris | Les chitinozoaires dans le Paléozoïque du sud-ouest de l'Europe (Cadre géologique -Etude systématique -Biostratigraphie)[END_REF] Genus Ancyrochitina Eisenack, 1955a Type species: Conochitina ancyrea Eisenack, 1931 Ancyrochitina alhajrii sp. nov. Paris (Plate X,2,4;Plate XI,6) v. 2005-Ancyrochitina alhajrii nomen nudum; Paris,pl. 4,.

Derivation of the name: this new species is dedicated to Sa'id Al-Hajri (Saudi Aramco) for our fruitful and long-term scientific collaboration.

Holotype: Plate X, 4; core 47, at 431.7 ft, IGR 72339 (O40).

Type locality: Baq'a-3 core hole, North Central Saudi Arabia.

Type stratum: Qusaiba Member of the Qalibah Formation; core 47, sample from 431.7 ft, early Telychian

Paratype: Plate X, 2; core 47, at 431.7 ft, IGR 72339 (O45).

Material: 239 specimens picked in the organic residues from cores 47 to 42 (Fig. 8) of the Baq'a-3 core hole.

Diagnosis: Ancyrochitina species with a well-developed cylindrical neck, a flaring collarette

A C C E P T E D M A N U S C R I P T

and a thickset conical chamber with a flat to slightly convex bottom; four to six long hollow processes pointing down from the margin; densely distributed minute hairs-like spines on the flanks and base of the neck.

Description: This medium-sized new Ancyrochitina species (mean vesicle length ca. 127 µm; see Table 7; Figs. 13a-b) shares all the characteristics of the genus as defined by Eisenack (1955a). The well-developed cylindrical neck terminates in a slightly flaring membranous collarette. A straight lip surrounds the aperture (Plate X,4a). The length of the neck and collarette exceeds that of the chamber (mean: lc/lp>1). A conspicuous flexure separates the neck from the chamber. No shoulder is observed on this thickset conical chamber, which diameter is larger than its length (i.e., Dp/lp>1). The bottom of the chamber is flat or slightly convex. This convexity is frequently accentuated during the compression of the vesicle, which causes the folding of the bottom wall inside of the chamber (Plate X, 4a). The margin is fairly sharp and bears four to six long and wide hollow processes (process length up to ca. 84 µm; diameter ca. 10 µm). These processes taper progressively toward their rounded distal end and are oriented more or less parallel to the longitudinal axis of the vesicle. The most discriminating character is the occurrence of randomly distributed thin hairs all over the vesicle. These slender hairs (diameter less than 0.5 µm; length ranging from 5 to 10 µm; see Plate X, 2b, 4b) are smaller towards the aperture. The granules stuck on the wall of some specimens (Plate X,4b) are "exotic" (not part of the ornamentation of the vesicle).

Measurements (Table 7; Figs. 13a-b). Discussion: Many Ancyrochitina species have a silhouette, or processes similar to those of A.

alhajrii sp. nov. The latter, however, is easily distinguished by its distinct hair-like vesicle ornamentation. The specimen (Plate XI,6), from the Baq'a-3 well (core 47 at 431.7 ft) does not clearly show the hair-like ornamentation of the chamber because organic matter coats the wall. The apparent branching of one process of this specimen is interpreted as an artifact (organic fragment stuck on the process). In some cases the hollow processes of A. alhajrii show a more or less cellular pattern like the processes of Plectochitina pseudoagglutinans.

The latter, however, lacks the hairy ornamentation on its chamber. Material: 35 specimens have been picked from the organic residues of cores 19 to 23 (Fig. 7;

Range and geographic

Table 20) from the Baq'a-4 core hole (about 350 specimens in the organic residue, as only 10% was picked; Table 2).

Diagnosis: Ancyrochitina species with a thickset conical chamber; fairly short neck terminated by a flaring collarette with serrate lips; smooth vesicle walls; six very long tapering processes briefly branched distally.

Description: This small sized species (mean vesicle length ca. 110 µm; Table 8; Figs. 14a-b) displays all the generic characters listed by Eisenack (1955a) for Ancyrochitina. The conical chamber has straight (Plate VIII,1) or slightly convex flanks (no shoulder) tapering toward a conspicuous flexure (the convexity of the flanks may be accentuated during the compression of the vesicle). The diameter and the length of the chamber are in the same range of values, ca. 80 to 90 µm. The short cylindrical part of the neck is prolonged with a well-developed collarette (collarette length close to the half of the length of the neck). The prosome is usually implanted in the base of the neck, which is therefore not fully compressed (correction factor of 0.9). Short spines (Plate VIII,1) or minute serrations (Plate VIII,6) border the lips surrounding the aperture. The vesicle wall is usually smooth; the granules on the holotype (Plate VIII, 1) result from amorphous organic matter adhering to the wall. The structure of the six long processes originating on the margin, sub-perpendicular to the vesicle axis, constitutes the most distinct character of this new species. These extremely long hollow processes (mean total length of the processes, including their branches = 55 µm, but reaching 87 µm for some specimens) taper very gently distally from a short conical base. The first branching occurs at about the last fourth of the total length. The resulting short branches are thinner and may subdivide up to four times. These successive short branches simulate a sort of distal fleuron;

Plate VIII,1,6).

Measurements (Table 8; Figs. 14a-b). Ancyrochitina with very long processes and without spines on the neck or on the chamber.

Among the closest species, A. ramosaspina Nestor, 1994 is larger and the branching of its

A C C E P T E D M A N U S C R I P T

processes occurs at about one half of their total length; each resulting branch is more robust.

Fairly similar chitinozoans (but with a different branching pattern) tentatively identified as A.

cf. ramosaspina occur in the lower Llandovery of the Murzuk Basin, Libya (Paris et al., 2012, pl. 4, figs. 2, 5-6). A. porrectaspina Nestor, 1994 has shorter processes with a different branching pattern (less numerous). A. longispina [START_REF] Achab | Les Chitinozoaires de l'Ordovicien supérieur, Formation de Vauréal et d'Ellis Bay de l'Ile d'Anticosti[END_REF] has a quite close silhouette.

However, its neck is better developed and the pattern of the branching of its long processes is also different (first branches perpendicular to the main trunk and occurring more proximally than in A. camilleae sp. nov.). Quite similar specimens previously identified as A. cf.

longispina have been recorded in the basal Silurian of the Kufra Basin, Libya (Paris, unpublished).

Range and geographic distribution: A. camilleae sp. nov. is only recorded in the Baq'a-4

well, in cores 19 to 23 from the Qusaiba Member of the Qalibah Formation. The corresponding strata are assigned to the Aeronian, and most likely to the late Aeronian as early Telychian graptolites of the guerichi Biozone occur quite close above these strata [START_REF] Zalasiewicz | Early Silurian (Llandovery) graptolites from Central Saudi Arabia: first documented record of Telychian faunas from the Arabian Peninsula[END_REF]. A camilleae is the index species of the chitinozoan subbiozone defined herein, in the upper part of the hemeri Biozone (Fig. 9).

Genus Plectochitina [START_REF] Cramer | Microplancton from three Palaeozoic formations in the Province of León (NW Spain)[END_REF] Type species: Plectochitina carminae Cramer, 1964. [START_REF] Jenkins | Chitinozoa from the Ordovician Sylvan Shale of the Arbuckle Mountains[END_REF]McClure, pl. XI, figs. 4-6, 8-9 (non fig. 10) 1988 -Plectochitina carminae [START_REF] Cramer | Microplancton from three Palaeozoic formations in the Province of León (NW Spain)[END_REF]McClure, pl. XI, fig. 12. ? 1991-Plectochitina pseudoagglutinans Taugourdeau, 1963;Al-Hajri, pl. 34, fig. 6 (non figs. 2-5). v. 1993-Plectochitina combazii Cramer, 1967;Paris, pl. 1, figs. 7-8. v. 2005 -Plectochitina alisawyiahensis nomen nudum;Paris, pl. 3, figs. 4,6;pl. 5, fig. 4;pl. 6, fig. 7;pl. 9, figs. 4-5, 8.

A C C E P T E D M A N U S C R I P T ACCEPTED MANUSCRIPT 64 1988 -Clathrochitina sylvanica

Derivation of the name:

The species name refers to the locality Al Isawyiah, in Saudi Arabia.

The ISWH EW-9 well drilled in this locality yielded the first specimens of the new species described here.

Holotype: Plate XII, 7, core 40, sample from 370.4 ft, IGR 72332 (P44/3).

Type locality: Baq'a-3 core hole, North Central Saudi Arabia. Material: 304 specimens have been picked from the organic residues from Baq'a-3, cores 16

to 56 (Fig. 8; Table 21) and 112 specimens from the organic residues from Baq'a-4, cores 7 to 17 (Fig. 7; Table 20). Several hundred additional specimens were available in the unpicked organic residues (see Tables 23) and in the ISWH EW-9 material (see below). Description: This spectacular and rather polymorphic species (Table 9;Plate XV,(4)(5)(6)(8)(9) shows all the generic characters of Plectochitina as defined by [START_REF] Cramer | Microplancton from three Palaeozoic formations in the Province of León (NW Spain)[END_REF],

i.e. a differentiated chamber/neck and cell-like processes. The vesicle is relatively small (average vesicle length: ca. 110 µm) with regard to the processes (lproc.: up to 130 µm length) (see Table 9 and Fig. 15b). The conical chamber has a flat base and a sharp margin.

The straight flank (no shoulder) passes to a short flaring neck through a weakly individualized flexure. This neck, including the collarette, represents close to the half of the vesicle length (processes not included) (Plate XV,(4)(5)9). A membranous flared lip surrounds the straight aperture. The vesicle walls are usually entirely smooth. A specimen with a few random spines on the flexure has been observed (Plate IX,7). The discriminating character is the very large crown of cell-like (vesicular) processes that runs around the margin. These numerous processes (about 15) are frequently much longer than the chamber. The diameter of these processes is quite variable, ranging from very wide, cylindrical or gently tapering isolated processes (e.g. Plate XV, 5) to slender elements anastomosing distally (Plate XV,8). The end of the processes are connected, either by a hollow rim (Plate XV,5) or more frequently arranged into three or four "buckle-like" structures around the margin (Plate XV,4,(8)(9). The processes originate directly from the margin wall, or from a membranous carina -like expansion (Plate XV,6) Measurements (Table 9; Figs. 15a-b). Several other Plectochitina species have been described in the Silurian of northern Gondwana regions. P. saharica [START_REF] Taugourdeau | Association de Chitinozoaires dans quelques sondages de la région de Edjelé (Sahara)[END_REF] from the early Silurian of SE Algerian Sahara is probably the most similar species. Its processes appear less well-developed and the available illustration does not allow a detailed comparison. P. fenesdiculae Al-Ameri, 1989, and P. lubnia (Al-Ameri, 1989), from the subsurface of Tripolitania (Libya) have longer necks and a different arrangement of their processes. P. combazii [START_REF] Cramer | Chitinozoans of a composite section of Upper Llandoverian to basal Lower Gedinnian sediments in northern Leon, Spain[END_REF] described in the Llandovery of Spain has numerous very thin processes. The provided illustration, however, does not demonstrate the presence of an external rim joining the distal end of the processes. P.

irregularis [START_REF] Cramer | Iberian Chitinozoans. 1. Introduction and summary of Pre-Devonian data[END_REF] described from the Lochkovian of Spain has very thin anastomosing processes and a better-developed neck. P. carminae is quite close to P.

A C C E P T E D M A N U S C R I P T

alisawyiahensis sp. nov., but it displays a different arrangement of its cell-like processes (fewer and thinner proximal branches; higher number of anastomosing knots). P.

sansalvadorensis [START_REF] Schweineberg | Silurische Chitinozoen aus der Provinz Palencia (Kantabrisches Gebirge, N-Spanien)[END_REF] from the Gorstian of Spain has processes with a similar anastomosing pattern, but its neck is much more developed than that in P. alisawyiahensis sp. nov.

Some Late Ordovician species have morphologies similar to P. alisawyiahensis sp. nov. The processes of P. concinna [START_REF] Achab | Les Chitinozoaires de l'Ordovicien supérieur, Formation de Vauréal et d'Ellis Bay de l'Ile d'Anticosti[END_REF] from the Late Ordovician of eastern Canada has quite a similar anastomosing pattern but the resulting "buckle-like" sets of processes are much shorter than those of P. alisawyiahensis sp. nov. P. sylvanica [START_REF] Jenkins | Chitinozoa from the Ordovician Sylvan Shale of the Arbuckle Mountains[END_REF] from the late Katian of Oklahoma has thinner processes with a different anastomosing pattern.

Range and geographic distribution: P. alisawyiahensis sp. nov. is extremely well-represented in the upper part of the Qusaiba Member of the Qalibah Formation in Saudi Arabia. It is quite abundant in the upper part of the Baq'a-4 well (Fig. 7; Table 20), where it occurs with A.

macclurei, and with graptolites of the guerichi Biozone (Fig. 9). P. alisawyiahensis sp. nov.

occurs irregularly along the investigated ca. 367.9 ft (113.2 m) thick sequence in the Baq'a-3 well (from core 56 to core 16 inclusive). It is a rather long ranging species, which is recorded in the macclurei through silurica chitinozoan biozones (Fig. 8; Table 21) of Telychian age . This new species has been reported under various names (see synonymy list) in other wells in Saudi Arabia [START_REF] Mcclure | Chitinozoan and acritarch assemblages, stratigraphy and biogeography of the Early Palaeozoic of Northwest Arabia[END_REF][START_REF] Al-Hajri | Systematics and biostratigraphy of Middle Ordovician to Lower Silurian chitinozoans of the Arabian Peninsula[END_REF]. The most productive samples were from ISWH EW-9 well, where the species is the dominant chitinozoan species in cutting samples from 3478 ft (1058 m) to 3603 ft (1096 m), and in a core sample from 3694.7 ft (1093.5 m). It is less abundant in the other investigated core samples at 1095.5 m to 1098 m [START_REF] Paris | Final report on chitinozoans from well ALISAWYIAH EW-9[END_REF]. This species and the associated chitinozoans allow now to firmly assign this part of the ISWH EW-9 well to the Telychian.

A C C E P T E D M A N U S C R I P T

chamber, where the width is usually greater than its length (mean Dp/lp close to 1.35), even after correction for compression (see Table 10). Randomly distributed granules or fairly large blunt cones occur on the vesicle wall, including the chamber bottom (Plate V,10). These granules fade away on the neck. Minute interrupted ridges present between the granules make a sort of irregular array with a more or less horizontal pattern (only visible by SEM). The subcylindrical neck ends with a membranous collarette flaring toward the aperture (straight to finely serrate lips). The chamber bottom is flat to slightly convex but depending on the compression pattern, its wall may be folded within the chamber (Plate V,10) or it can be totally tilted (Plate V,2). Six to eight processes of variable length and with a "spongy" to celllike (vesicular) internal structure (visible in transmitted light) are located on the margin. They are bi-rooted (Plate V, 2), occasionally multi-rooted and rarely simple with a widened base.

These processes are very brittle and only the proximal part may be preserved. For that reason the average length (ca. 20 µm) of the processes given on Table 10 is largely under-estimated.

When fully preserved the tapering distal part of the processes represents at least two third of their total length (Plate V, 2).

Measurements (Table 10; Figs. 16a-b). between brackets; *correction factor: 0.8; ** correction factor: 0.7).

Discussion: When collecting the biometric data with a transmitted light microscope at high magnification, the processes of this chitinozoan show constant spongy internal structure. [START_REF] Cramer | Microplancton from three Palaeozoic formations in the Province of León (NW Spain)[END_REF] and Paris et al. (1999) regarded this character as diagnostic for Plectochitina.

The former generic assignment of this new species to Ancyrochitina, based exclusively on SEM, is therefore modified here (see synonymy). Al-Hajri (1991, pl. 30, fig. 5) illustrated a chitinozoan sp. nov. with a silhouette, multi-based processes and dimensions fitting with the present definition P. alnaimi sp. nov. (see synonymy).

Plectochitina alnaimi sp. nov. belongs to the Plectochitina forms with bi-or multi-rooted relatively short processes. Such taxa are quite common in the early Silurian and may be confused with Ancyrochitina species illustrated by SEM. A. diabolo Eisenack, 1937 from the Silurian of the Baltic area has a similar silhouette, but its robust processes are not described as bi-rooted or with a spongy internal structure. A. magna [START_REF] Nestor | New Wenlockian species of Conochitina from Estonia[END_REF] from the Wenlock of Baltoscandia is much larger and has processes with a wider proximal part. A. obesa Tsegelnjuk, 1982 from the early Wenlock of Podolia has a similar silhouette, but not bi-rooted processes. A. spinosa Al-Ameri, 1989 has a conspicuous shoulder and no bi-rooted processes.

A. alhajrii sp. nov. is differentiated from P. alnaimi sp. nov. by the lack of processes with a spongy to cell-like structure, and because of its hair-like ornamentation covering the vesicle walls.

Range and geographic distribution: Plectochitina alnaimi sp. nov. is extremely abundant in most of the samples from the Qusaiba-1 core hole (Fig. 6; Table 19). It is the dominating species of the hemeri Biozone (70% of the chitinozoans recorded at 140.1 ft in the type

A C C E P T E D M A N U S C R I P T stratum).
The species, which has apparently its LAD at 136.5 ft, is already present but less abundant in the upper part of the qusaibaensis Biozone penetrated by the Qusaiba-1 core hole (Fig. 6; Table 19). Surprisingly it is missing in the main part of the alargada Biozone (Fig. 6).

In the Qusaiba-1 core hole, the coexistence of P. alnaimi sp. nov. with graptolites of the convolutus Biozone supports a mid-Aeronian age for the range of the species. If one accepts the proposed synonymy, the new species is also present in northern Saudi Arabia, in sample 10 from the "QA" well of the Tabuk area [START_REF] Al-Hajri | Systematics and biostratigraphy of Middle Ordovician to Lower Silurian chitinozoans of the Arabian Peninsula[END_REF].

Derivation of the name:

The species is dedicated to my wife Jacqueline Paris for her patient support during my career.

Holotype: Plate XIV, 6, core 34, sample from 306.0 ft, IGR 72323 (P43).

Type locality: Baq'a-3 core hole, North Central Saudi Arabia.

Type stratum: Qusaiba Member of the Qalibah Formation; core 34, sample from 306.0 ft, early Telychian.

Paratype: Plate XIV, 4, core 34, sample from 306.0 ft, IGR 72323 (R43).

Material: 52 specimens were picked from the organic residue of core 34 of the Baq'a-3 core

A C C E P T E D M A N U S C R I P T
hole (Fig. 8; Table 21). More than one hundred additional specimens are available in the remaining organic residue (see Table 3) and in the material from the ISWH EW-9 well (see below).

Diagnosis: Plectochitina species with granulose flanks; conical chamber with a welldeveloped cylindrical neck flaring around the aperture; rounded margin with a crown of ca. 20 to 30 very short processes; these spongy processes are simple or have short branches at their distal end.

Description: This medium sized chitinozoan (L ranging from ca. 74 to 174 µm; mean length: 130 µm; holotype length: 144 µm; see Table 11) has a conical chamber with rapidly tapering flanks and a flat base. The vesicle wall is rugose to granular. No shoulder is present on the chamber but a conspicuous flexure separates the tapering straight flanks from a welldeveloped neck (mean value of the ratio lc/L close to 0.61; see Fig. 17). Straight or very finely serrate lips surround the aperture of this cylindrical to gently flaring neck (Plate XIV,4a,6a). Occasionally, a membranous expansion of the prosome (with septa) extends out of the aperture (Plate XIV,6a). This prosome is located deeply within the neck (proximal part originating near the flexure). The rounded margin carries a crown of numerous (usually 20 to 30) short spongy processes (length ranging from 3.5 to 13.4 mm; mean= 7.3 mm). In a few cases, a very short membrane (less than 3 µm) joins the base of these processes, which may branch in a fleuron-like structure at their distal end (Plate XIV,4b). In other cases the processes taper or have a blunt end (Plate XIV,6b). In transmitted light microscope, the short processes display a spongy structure, which supports an assignment to Plectochitina, rather than to Ancyrochitina (see discussion below).

Measurements (Table 11; Figs. 17a-b). Discussion: Because the occurrence of a membrane joining the base of the processes of some specimens this species could be assigned to Anthochitina. In the present material this character is very unusual and the most common feature is the existence of processes directly fixed to the margin, such as on the holotype (Plate XIV,6b). A generic assignment to Ancyrochitina is also conceivable, but the spongy structure of the processes better supports the assignment to Plectochitina, even if the occurrence of very short and numerous processes is an uncommon feature for this genus. [START_REF] Al-Hajri | Systematics and biostratigraphy of Middle Ordovician to Lower Silurian chitinozoans of the Arabian Peninsula[END_REF]pl. 30, fig. 4) illustrated a chitinozoan with a membranous expansion (ending with spines) around the margin. This form from the "QI" well (Qasim area) was assigned to Clathrochitina sp. by [START_REF] Al-Hajri | Systematics and biostratigraphy of Middle Ordovician to Lower Silurian chitinozoans of the Arabian Peninsula[END_REF]. It has not been included in the synonymy of P. jacquelineae sp. nov. in spite of its similar outline because of the occurrence of the spiny membrane also present in some Anthochitina species recorded in the Qusaiba-1 core hole (e.g., Anthochitina primula from core 15 at 145.9 ft; Plate V, 11-12).

In the ISWH EW-9 well, chitinozoans with a crown of frequently bi-rooted and longer Range and geographic distribution: P. jacquelineae sp. nov. is quite abundant in the upper part of the Qusaiba Member of the Qalibah Formation in Saudi Arabia. It is restricted to core 34, at 306.0 ft, from the Baq'a-3 core hole (Fig. 8; Table 21) where it occurs with graptolites of the turriculatus s.l. Biozone of early Telychian age (Fig. 9). The species was also recorded in the ISWH WE-9 well (cuttings from 1006 m to 1070 m) under the name "Pl. jiangsuensis" but its FAD is difficult to locate precisely in this well because many specimens are likely caved. If one accepts the synonymy proposed here, P. jacquelineae sp. nov. is also present in the Qusaiba Member of the subsurface of the Tabuk and Qasim area [START_REF] Mcclure | Chitinozoan and acritarch assemblages, stratigraphy and biogeography of the Early Palaeozoic of Northwest Arabia[END_REF].

A C C E P T E D M A N U S C
Plectochitina lucasi sp. nov. Paris (Plate XV,3,7) A C C E P T E D M A N U S C R I P T slender hollow process. This pattern is not visible on the paratype (Plate XV, 3) because the chamber walls hide the proximal connection of the preserved processes. The presence of these multi-rooted processes and their "spongy" to cell-like internal structure is easily visible in transmitted light microscopy. The processes have a peculiar profile with a curved short proximal part oriented at 45° with regard to the longitudinal axis of the vesicle and becoming parallel to this axis in the remaining part ("lyre-like" aspect).

Measurements (Table 12; Figs. 18a-b). -b) has a thickset conical chamber with walls tapering rapidly toward a conspicuous flexure. The flanks are straight (no shoulder observed). The margin is rounded but this character as well as the flat bottom may be variously modified during the compression (Plate IX,1,3). The cylindrical neck is short (less than half of the total vesicle length) and shows a straight to weakly serrate aperture. The flaring aspect of the neck of the specimen illustrated on Plate IX, 3 is due to its twisted and folded wall. The discriminating character is the spiny ornamentation randomly distributed on the vesicle. These spines are generally simple, but some of them have a widened proximal part or a "lambda-type" insertion on the vesicle wall. These tapering spines or hairs (Plate X,5b) are quite long (maximum length up to 15 µm). This ornamentation is better developed on the margin and on the lower half of the flanks. The spines are much shorter on the neck and on the bottom of the chamber and they are simple cones near the aperture (Plate IX,1).

Measurements (Table 13; Figs. 19a-b). Discussion: Angochitina and Fungochitina genera are both spiny Lagenochitinidae, which have respectively an ovoid and a conical to lenticular chamber (Paris et al., 1999).

Fungochitina species normally have a flat bottom and a fairly sharp margin. In the present material, depending on the vesicle compression, the chamber bottom also seems flat, but this character is possibly accentuated by folding of the base into the chamber (Plate IX, 1; Plate X, 5a). The lateral compression has also accentuates the apparent width of the holotype and a coeff. of 0.7 has been used when restoring its chamber diameter (see Table 13). This small species could alternatively be attributed either to Fungochitina or to Angochitina and originally it was as a nomen nudum assigned to Angochitina because the hair-like ornamentation is more commonly observed in this genus. However, during the course of a revision of the Angochitininae, the new species merrelli is attributed to Fungochitina, in order to fit with the "compact" diagnosis of this genus in Paris et al. (1999). Al-Hajri (1991, pl. 29, figs. 2-4;pl. 30, figs. 1-2, 4) has illustrated and described specimens similar to F. merrelli sp.

nov. Some of these specimens display longer spines on the margin (e.g. pl. 29, figs. [2][3][4] suggesting an assignment to Ancyrochitina. The two specimens from the Qusaiba Member of the Tabuk and Qasim areas illustrated by [START_REF] Mcclure | Chitinozoan and acritarch assemblages, stratigraphy and biogeography of the Early Palaeozoic of Northwest Arabia[END_REF] under the name "Sphaerochitina lepta" (see synonymy) seem comparable to F. merrelli sp. nov. The illustration, however, does not permit a confident assignment to our new species.

A C C E P T E D M A N U S C R I P T

The silhouette of F. merrelli sp. nov. is comparable with that of some Devonian Fungochitina species, such as F. pilosa [START_REF] Collinson | Chitinozoan-Faunule of the Devonian Cedar Valley Formation[END_REF] or F. hispida (Taugourdeau and de Jekhosky, 1960), which have more robust spines and longer necks. F. bernesgae [START_REF] Cramer | Chitinozoans of a composite section of Upper Llandoverian to basal Lower Gedinnian sediments in northern Leon, Spain[END_REF] from the Silurian of Spain has shorter spines and a better developed neck. F.

illinoisensis [START_REF] Butcher | Late Ordovician-Early Silurian chitinozoans from north-eastern Illinois, USA[END_REF] from the Rhuddanian of the Illinois, USA, has a larger vesicle, more robust conical spines and a flared collarette.

In the Qusaiba-1 core hole, specimens provisionally identified as Fungochitina? sp. aff. F. merrelli sp. nov. (Fig. 6; Table 19) were recorded in core 22 at 210.9 ft (Plate III, 4a-b) and in core 15 at 145.9 ft (Plate V,4,. Their spiny ornamentation is more densely distributed than in the F. merrelli sp. nov., their ratio Dp/dc is lower and the spines seem better developed on the margin (Plate III,4b). The last character to some extent evokes Ancyrochitina species (see [START_REF] Mcclure | Chitinozoan and acritarch assemblages, stratigraphy and biogeography of the Early Palaeozoic of Northwest Arabia[END_REF].

Range and geographic distribution: F. merrelli sp. nov. is recorded in the upper part of the Qusaiba Member in the Baq'a-4 and Baq'a-3 core holes (Figs. [7][8]. This restricted distribution makes it suitable as the index species of the merrelli total-range subbiozone characterizing the upper part of the macclurei Biozone. The occurrence of F. merrelli with graptolites of the guerichi Biozone allows an age assignment of the corresponding strata to the early Telychian. F. merrelli sp. nov. is possibly represented (see synonymy above) in the Qusaiba Member of the Qalibah Formation in well "QA" of the Tabuk area [START_REF] Al-Hajri | Systematics and biostratigraphy of Middle Ordovician to Lower Silurian chitinozoans of the Arabian Peninsula[END_REF][START_REF] Mcclure | Chitinozoan and acritarch assemblages, stratigraphy and biogeography of the Early Palaeozoic of Northwest Arabia[END_REF].

Genus Muscochitina [START_REF] Paris | Les chitinozoaires dans le Paléozoïque du sud-ouest de l'Europe (Cadre géologique -Etude systématique -Biostratigraphie)[END_REF] Type species: Muscochitina muscosa [START_REF] Paris | Les chitinozoaires dans le Paléozoïque du sud-ouest de l'Europe (Cadre géologique -Etude systématique -Biostratigraphie)[END_REF] A C C E P T E D M A N U S C R I P T Muscochitina olivieri sp. nov. Paris (Plate I,1,4,6) v. 1991 -Sphaerochitina sp. indet.; Paris, pl. 1, figs. 7a-b. v. 1992 -b) has a well-developed flaring neck separated from the chamber by a conspicuous flexure. The shoulder is fairly weak as the chamber is ovoid to sub-spherical, especially when the wall is folded during the compression of the vesicle (Plate I,4a). The neck gently flares aperturalwards, and represents one third to one half of the total vesicle length (length the neck

A C C E P T E D M A N U S C R I P T
of the holotype: lc= 67 µm). The lips around the aperture are straight or slightly notched (Plate I,1a). The distinctive character of this species is the peculiar elevated mesh covering the whole vesicle. This ornamentation is composed of finial structures (fleuron-like) made of thin radial threads diverging from a central connection point or knot (Plate I,1b,. These connection points are fixed to the vesicle wall through very short pillars fairly regularly dispersed on the vesicle. The slender threads (up to ten threads per finial structure) taper distally (Plate I,4c). This mesh-like ornamentation fades away on the neck. The mesh may trap small particles (Plate I,1b, and thus simulates a granular wall surface in transmitted light microscopy.

Measurements (Table 14; Figs. 20a-b). [START_REF] Paris | Final report on chitinozoans from well UDAYNAN. 1[END_REF], and from core 20, at 16872 ft depth in the TINT-2 well [START_REF] Paris | Final report on the chitinozoans recorded in well TINAT[END_REF]. The occurrence of M. olivieri sp. nov. allows a more refined correlation of parts of these two deep wells within the mid-Aeronian.

Order Operculatifera [START_REF] Eisenack | Chitinozoen und andere Mikrofossilien aus der Bohrung Leba[END_REF] Family Desmochitinidae [START_REF] Eisenack | Neue Mikrofossilien des baltischen Silurs I[END_REF], emend Paris, 1981 Subfamily Desmochitininae [START_REF] Paris | Les chitinozoaires dans le Paléozoïque du sud-ouest de l'Europe (Cadre géologique -Etude systématique -Biostratigraphie)[END_REF] Genus Bursachitina [START_REF] Taugourdeau | Les Chitinozoaires, techniques d'études, morphologie et classification[END_REF] A C C E P T E D M A N U S C R I P T silhouette of the vesicle. The operculum corresponds usually to a fairly long cylindrical plug composed of a disc with a thin-walled rica (total length up to 30 µm). In specimens with a well-developed collarette, this operculum is located quite deep, near the chamber-collarette junction. In the available material, the collarette and most of the chamber are completely flattened but the fairly sharp margin, because of its thicker walls is less deformed. The differential compression due to differences in the thickness of the walls resulted in an accentuation of the convexity of the flanks (normally straight or slightly convex). As a consequence the wider part of the chamber is no longer on the margin (its original position before this differential compression) but moved towards the middle part of the chamber. The chamber bottom is slightly convex, but the original convexity is accentuated during the compression that caused the tear near the central callus of the lower vesicle (Plate VIII,3).

The callus has a wide rim (diameter close to 20 µm) surrounding a slightly depressed area. occurs in long chain-like structures compressed laterally (Plate III,9;Plate VI,12). In that case, each vesicle looks like a very thickset barrel (L/Dp close to 0.5; see Table 16 and Fig. 22a). Important variations of the size and of the shape of the vesicles are noticed between different chain-like structures. This is obvious on Figure 22a where the four chain-like structures used for the measurements appear as separate clusters. A slight difference is also recorded along each "chain" as illustrated on Figure 22b (see also Plate VI,12a). Closer

Measurements (

connected individuals occur at one extremity of the chain whereas the larger and betterseparated vesicles are at the end. This suggests that these chain-like structures correspond to early stages of a lay out (likely intra-oviduct connected ovules, according to the interpretation given by [START_REF] Paris | Biological interpretation and paleobiodiversity of a cryptic fossil group: "the chitinozoan animal[END_REF]. No neck or collarette are present around the large aperture with a diameter about half size of the chamber, and which is closed by a discoid operculum (Plate III,9). The antiapertural and apertural poles are usually difficult to identify because the folding and the buckling of the chamber hide the aperture in the catenary structures. The latter are extremely common in the recovered organic residues and indicate a strong intra-vesicle linkage. One of the distinctive features of this species is the spongy to felt-like outer layer extending laterally when the vesicles are totally flattened. This character is more visible in transmitted light microscopy. When the vesicles are severely compressed laterally, this unstuck thin-walled layer wraps the chamber and appears as a less opaque area surrounding chamber walls, especially along the flanks. This fairly transparent zone (only outer layer involved) can be shifted on one side of the vesicle during the compression and in that case it may be easily confused with the carina of a Pterochitina species (see discussion below). Discussion: It may be tempting to assign the specimens recovered in core samples from the Qusaiba-1 and Baq'a-3 core holes either to Pterochitina or to Calpichitina, as these two genera have also a lenticular chamber (Paris et al., 1999). An extensive discussion of Cutichitina and Pterochitina, which may be easily confused when the vesicle are compressed, is given by Paris in Rickards et al (2010, p. 115). Concerning the Qusaiba material, the threedimensional reconstruction of the flattened vesicles leads to a preferred assignment to Cutichitina Achab, Asselin and Soufiane, 1993, even if this genus was created for the Desmochitinidae with an ovoid chamber (so far no genus has been created for the chitinozoans with a lenticular chamber surrounded by a detached velum [START_REF] Paris | Final report on chitinozoans from well UDAYNAN. 1[END_REF][START_REF] Paris | Final report on the chitinozoans recorded in well TINAT[END_REF]. Calpichitina [START_REF] Wilson | Calpichitina scabiosa, a new Chitinozoan from the Sylvan Shale (Ordovician) of Oklahoma[END_REF] was indeed an alternative generic assignment for the Qusaiba specimens because their lenticular chamber (see synonymy list).

Measurements (

Moreover, Calpichitina may have a spongy surface, e.g., C. spongiloricata [START_REF] Wrona | Upper Silurian -Lower Devonian Chitinozoa from the subsurface of southeastern Poland[END_REF] but no completely separated membrane is reported in this genus. Other Calpichitina species have partly folded outer layer, e.g. C. squamosa [START_REF] Laufeld | Silurian Chitinozoa from Gotland[END_REF] from the Ludlow of Gotland, or C. velata [START_REF] Wrona | Upper Silurian -Lower Devonian Chitinozoa from the subsurface of southeastern Poland[END_REF], from the upper Silurian of Poland. Both species have a membranous collarette and are not commonly arranged in resistant chain-like structures like Cutichitina minivelata sp. nov. The specimen recorded in the Baq'a-3 core hole at 350.0 ft (Plate XIII,6) has a spongy outer layer stuck on the chamber. It is tentatively assigned to Cutichitina minivelata sp. nov.

Range and geographic distribution: Cutichitina minivelata sp. nov. is a rather long ranging species, which is irregularly distributed in the Qusaiba Member of the Qalibah Formation in the Qusaiba-1 and in the Baq'a-3 core holes (Figs. 6 and8). The corresponding strata are assigned to the Aeronian and to the Telychian pro parte. Based on the proposed synonymy, the new species is most likely present in the Qusaiba Member of the Qalibah Formation in the subsurface of the Qasim area in samples 6a and 7a from the "QU" well [START_REF] Al-Hajri | Systematics and biostratigraphy of Middle Ordovician to Lower Silurian chitinozoans of the Arabian Peninsula[END_REF]. C. minivelata sp. nov. is abundant in the upper part of core 17 from the UDYN-1 well and in cores 17 to 20 in the TINT-2 well [START_REF] Paris | Final report on chitinozoans from well UDAYNAN. 1[END_REF][START_REF] Paris | Final report on the chitinozoans recorded in well TINAT[END_REF]. Based on the present calibration of the chitinozoans of the Qusaiba Member by graptolites [START_REF] Zalasiewicz | Early Silurian (Llandovery) graptolites from Central Saudi Arabia: first documented record of Telychian faunas from the Arabian Peninsula[END_REF], the corresponding strata are assigned to the mid-Aeronian to early Telychian (Fig. 9).

Subfamily Pterochitininae [START_REF] Paris | Les chitinozoaires dans le Paléozoïque du sud-ouest de l'Europe (Cadre géologique -Etude systématique -Biostratigraphie)[END_REF] Genus Armoricochitina [START_REF] Paris | Les chitinozoaires dans le Paléozoïque du sud-ouest de l'Europe (Cadre géologique -Etude systématique -Biostratigraphie)[END_REF] Type species: Linochitina ? ceneratiensis [START_REF] Paris | Les Chitinozoaires[END_REF]. Material: 166 picked vesicles from the organic residues from the Baq'a-3 cores 36 to 45 (Fig. 8; Table 21) and several hundred specimens in the corresponding unpicked organic residues (see Table 3).

Armoricochitina crassicarinata

Diagnosis: Small Armoricochitina species with a thick-walled ovoid chamber; weakly corrugated walls; short membranous collarette; thickened carina below the margin.

Description: This species shares all the characters of the genus Armoricochitina. The ovoid to pear-shaped chamber has a slightly convex bottom but this aspect is frequently hidden when the bottom wall is folded inwards the chamber in laterally compressed vesicles. The larger diameter is situated over the lower third of the chamber. The chamber width (Dp) represents about three quarter of the vesicle length (L) (Fig. 23a Material: Sixteen picked specimens from the organic residue from 250.5 ft (core 27) and 62 specimens from 150.4 ft (core 16) in the Baq'a-3 core hole (Table 3, Fig. 8); about 600 specimens in the corresponding unpicked organic residues.

Diagnosis: Armoricochitina species with a conical to pear-shaped chamber; walls fairly thick with a weakly corrugate surface; membranous carina located closely below the margin; chamber bottom gently convex.

Description: This new species has gently tapering flanks with an inflexion of their convergence over the middle part of the chamber. Because important variations in the development of the neck/collarette (lcoll. is measured from this inflexion to the border of the lips; Table 18; Fig. 24b), the total length of the vesicle (L) shows greater variations than the chamber width (Table 18; Fig. 24a). The sigmoid profile of the flanks may be deeply

A C C E P T E D M A N U S C R I P T

modified by differential compression of the vesicle. When totally flattened (Plate XV, 1), the maximum width of the chamber fits with the margin, whereas when the lower part of the chamber is not totally flattened the maximum width is situated at the lower forth or fifth of the vesicle length (Plate XVIII,5). The surface of the rather thick chamber wall displays small corrugations generating a "wavy" pattern more or less parallel to the margin. The thickness of the chamber wall (ca. 2.5 µm) is visible on lateral cracks of the compressed holotype (Plate XV,1). A membranous collarette with straight lips surrounds the aperture. The chamber bottom is slightly convex but this character may be modified when the bottom wall is folded into the chamber in compressed vesicles. A membranous carina (mean length ca. 13 µm) is located just below the margin. This critical taxonomical character is sometime difficult to evaluate on compressed specimens, e.g. the holotype (Plate XV, 1), or when the carina is folded up on the margin (Plate XVIII,5). A circular scar (not visible on the illustrated material) occurs on the bottom of the chamber. between brackets; *correction factor: 0.8; ** correction factor: 0.7).

Measurements (

Discussion: An assignment to the genus Armoricochitina rather than to Cingulochitina is preferred because the widest part of the chamber is above the margin. In addition, the chamber wall is fairly thick and displays micro-corrugations. Both are features uncommon in Cingulochitina species.

A. gengi sp. nov. is similar to A. crassicarinata sp. nov., but the latter has a distinct thick rimlike carina. A. panzuda [START_REF] Cramer | Microplancton from three Palaeozoic formations in the Province of León (NW Spain)[END_REF] from the Emsian of northern Gondwana regions [START_REF] Paris | Toward a global biozonation of Devonian chitinozoans[END_REF] has a carina located well below the margin. A. gengi sp. nov. resembles several Silurian Cingulochitina species with a short carina. C. burdinalensis [START_REF] Verniers | Calibration of Chitinozoa versus graptolite biozonation in the Wenlock of Built Wells district (Wales, U. K.), compared with other areas in Avalonia and Baltica[END_REF]C. bouniensis Verniers, 1999 have a more ovoid chamber. C. serrata [START_REF] Taugourdeau | Répartition et description des Chitinozoaires siluro-dévoniens de quelques sondages de la C.R.E.P.S., de la C.F.P.A. et de la S.N. Repal au Sahara[END_REF]) has a smooth wall, a more convex chamber bottom and a mucron.

The chitinozoan "chain" recorded at 350.1 ft in the Baq'a-3 well, and provisionally identified the membranous carina or the corrugated wall surface are less obvious (Plate XVII: 1a,2a).

The large circular rim on their convex bottom (Plate XVII,1b,2b) suggests that they were usually arranged in chain-like structures such as the "twins recorded" at 350.5 ft (Plate XIII,2).

Range and geographic distribution:

In the Baq'a-3 core hole, A. gengi sp. nov. is recorded in the upper part of the Qusaiba Member of the Qalibah Formation from core 27 to core 16 22.

Table 1. Data concerning the lithology, the processing, and the faunal content of the core samples processed in the Silurian part of the Qusaiba-1 core hole.

Table 2. Data concerning the lithology, the processing, and the faunal content of the core samples processed in the Baq'a-4 core hole.

Table 3. Data concerning the lithology, the processing, and the faunal content of the core samples processed in the Baq'a-3 core hole.

Table 19. Chitinozoans of the early Rhuddanian and mid-Aeronian samples from the Qusaiba Member of the Qusaiba-1 core hole plotted on a stratabug diagram. The author(s) and the year of publication of the recorded chitinozoans taxa are given on Table 22.

Table 20. Chitinozoans of the mid-Aeronian and early Telychian samples from the Qusaiba Member of the Baq'a-4 core hole plotted on a stratabug diagram. The author(s) and the year of publication of the recorded chitinozoans taxa are given on Table 22.

Table 21. Chitinozoans of the Telychian samples from the Qusaiba Member of the Baq'a-3 core hole plotted on a stratabug diagram. The author(s) and the year of publication of the recorded chitinozoans taxa are given on Table 22.

Table 22. List of the chitinozoan taxa recorded in the Qusaiba-1, Baq'a-3 and Baq'a-4 core holes. The chitinozoan species cited in the text but not present in the studied material have an asterisk. The compression affecting the chamber diameter is not corrected (Holotype: red diamond). Note the thickened rim corresponding to the margin. ( 9): IGR 72253 (O45).

Captions of the figures

5.

Angochitina qusaibaensis Paris and Al-Hajri, 1995. 251.10 ft;IGR 72253 (Q44).

Possibly a new form with a long slender neck acting as a transitional form between A. qusaibaensis and "true" A. hemeri. The prosome of these specimens is prolonged by a thin walled tubular structure (see also Plate II,[6][7][8][9].

  assignment. None of the species recorded in the obtusa Biozone provide accurate chronostratigraphical information. The absence of early Sheinwoodian chitinozoans, such as Margachitina margaritana, suggests that the obtusa Biozone still belongs to the Telychian, and probably to the mid to late Telychian, as graptolites (turriculatus s.l. Biozone) are still present at 303 ft. The graptolites, and especially the retiolitids recovered in the palynological residue from 229.7 ft in Baq'a-3 should give a better tie with the standard graptolite zonation of the Telychian. The obtusa Biozone is at present tentatively correlated with levels within the griestoniensis to spiralis graptolite zones.

  usable in the northern Gondwana regions (north and west Africa, southern parts of Europe, the Arabian Plate and western Iran). In addition, five subbiozones of more local value (Arabian Plate or beyond) are proposed (Fig.9). One characterises the upper part of the hemeri Biozone (the camilleae subbiozone). Two other biostratigraphic subdivisions (the merrelli and the crassicarinata subbiozones) are part of the macclurei Biozone. The two remaining (jacquelineae and lucasi subbiozones) occur within the obtusa Biozone.The chitinozoans recorded in the lowermost part of the Qusaiba Member in the Qusaiba-1 core hole, permit identification of a distinctive early Rhuddanian chitinozoan assemblage ("Assemblage 1" inParis et al., this volume). No formal biozone name is proposed for this assemblage located immediately above the top of the Sarah Formation (Figs.3 and 6) because apart from B. pseudarabiensis it does not contain key chitinozoan species of the lower Llandovery chitinozoan biozonation. Nevertheless, based on similar chitinozoan assemblages coexisting with early Rhuddanian graptolites in other northern Gondwana localities, the association with dominant C. caputoi and B. pseudarabiensis is considered diagnostic of the basalmost Silurian (see discussion inParis et al., this volume). Because the immediately overlying strata yield chitinozoans of the qusaibaensis Biozone associated with graptolites of the convolutus graptolite Biozone, a significant hiatus (most of the Rhuddanian and Aeronian pro parte) is recognized in the lower part of the Qusaiba Member (core 27 at 254.5 ft; Fig.6).

  A C C E P T E DM A N U S C R I P T 140.6 to 40.1 ft) of the Baq'a-4 well, where the chitinozoans of the macclurei Biozone occur with graptolites of the guerichi Biozone. The middle and upper part of the biozone is documented from the lower part (cores 56 to 36, i.e. from 518.3 ft to 330.4 ft) of the Baq'a-3 core hole. In this well, the chitinozoans are associated with graptolites of the turriculatus s.l.

  ) in order to depict possible relationships between the lithology and the abundance of the chitinozoans. The lithology is fairly constant through the investigated part of the Qusaiba Member dominated by greenish to grey shale. With the exception of the carbonaceous shale at 254.8 ft and of a thin sandy bed (254.5 ft to 253.5 ft) in the Qusaiba-1 core hole, only minor lithological variations are noticed, especially increases of the silt fractions (e.g., at 330.4 ft and 306.0 ft in Baq'a-3, or at 60.1 ft and 40.1 ft in Baq'a-4) or the occurrence of silty to fine sandy laminae (e.g., at 132.05 ft in Qusaiba-1, at 130.0 ft in Baq'a-3, and at 269.0 ft or 240.7 ft in Baq'a-4). The most significant increase of the grain size is noted in core 14 (130.0 ft) in Baq'a-3. There is not an obvious relation between the grain size or the colour of the sediment when compared to the abundance of the chitinozoans (expressed in specimens per gram of rock). One would expect to have the highest abundances in the shaly facies. The highest recorded values are in core 14 from Qusaiba-1, respectively at 140.1 ft in the grey greenish shale (3920 chitinozoans per gram of rock) and at 136.5 ft, in the grey greenish siltstone (3080 chitinozoans per gram A C C E P T E D M A N U S C R I P T

  . 8), possibly due to their delicate ornamentation. Such low energy depositional settings are also required for the preservation of thin-walled delicate structures as the "sleeve" extended externally from the prosome of A. qusaibaensis. The fragile aggregates of crushed Cyathochitina recorded at 245.8 ft in the Qusaiba-1 well, and interpreted as coprolites, may have survived because they were produced in situ in the sediment (occurrence of small internal bioturbation). Other species are representative of open and deeper marine environments e.g. Angochitina hemeri, Angochitina macclurei. They are the dominating taxa in the less diversified assemblages recorded in the TINT-2 well, corresponding likely to a more distal environment setting. The slight lithological changes observed in the Baq'a-3 and Baq'a-4 core holes, however, have no real impact on the abundance of A. macclurei (Tables2-3 and Figs. 7

  penetrated by the Qusaiba-1, the Baq'a-4 and the Baq'a-3 core holes are extremely diverse and contain abundant and well-preserved chitinozoans. These shallow cores allowed overcoming of the effects of the deep weathering that affects the outcrop samples and precludes the use of palynomorphs for their dating. The present data permit establishing a precise biozonation for the chitinozoans in the material from the type area of the Qusaiba Member and from the neighbouring Baq'a area. The identified biozones provide excellent correlation with the subsurface sequences of the central and north-eastern parts of Saudi Arabia. Direct calibration by associated graptolites allows precise age assignment in terms of the standard graptolite biozones and of Silurian stages.A significant hiatus representing most of the Rhuddanian and the lower part of the Aeronian is documented in the lower part of the Qusaiba Member in the Qusaiba-1 core hole. The hiatus is located above the basal part of the Qusaiba Member, which yields very abundant earliest Rhuddanian chitinozoans immediately above the last glacially related Baq'a Sand Member of the Sarah Formation (see discussion inParis et al., this volume). This hiatus corresponds either to a gap (but no erosion or palynomorph reworking is observed) or to a highly condensed sequence as suggested by the abundant bioturbation developed in a thin sandy bed above the hiatus. The main part of the Qusaiba Member was deposited in open and low energy marine environments as demonstrated by the preservation of very delicateA C C E P T E D M A N U S C R I P Tstructures in the chitinozoans (e.g., "sleeve" of A. qusaibaensis, clusters of A. macclurei, coprolites consisting of fragmented Cyathochitina).

  . Owing to the variations recorded in the present population of S. geerti sp. nov., the UDYN-1 specimens are included in the synonymy list of the new species. Other Spinachitina specimens recorded in well "QA"(Al-Hajri, 1991, pl. 25, figs. 1-4; see synonymy above) could also belong to S. geerti sp. nov. because the tiny granules occurring on their transparent neck may represent spine remains.Range and geographic distribution:In the Baq'a-4 core hole, S. geerti sp. nov. has been recorded exclusively in cores28 (240.7 ft) where it is abundant, and in core 19 (163.0 ft) (very rare; see Fig.7). The corresponding strata belong to the upper part of the hemeri Biozone, which is assigned to the Aeronian, most likely to the mid-late Aeronian (see discussion above). Van Grootel (1990) recorded his "Spinachitina spinosa" nomen nudum in samples from the subsurface of the Brabant Massif (Belgium) in the Kortrijk and Steenkerke 50E-134 (267.0 and 323.0 m) core holes. According toVan Grootel (1990, p. 80) the corresponding strata range from the Aeronian to the Telychian (middle part of the sedgwickii to the crispus graptolite zones).

Diagnosis:

  Plectochitina species with flat-based conical chamber and short cylindrical neck flaring around the aperture; fairly sharp margin carrying a crown of long and wide cell-like processes; these simple or anastomosed processes are connected at their distal end, either as A C C E P T E D M A N U S C R I P T several separated sets, or all together.

Table 9 :

 9 figs.4-6, 8-9,11) from the subsurface of Tabuk and Qasim areas show the same variable

  Fig.21a). The rather thickset chamber (Dp close to lp; Fig.21b) is conical with flanks gently tapering toward the collarette. This collarette (lcoll. ranging from 10 µm to 50 µm) has membranous finely serrate lips. The imprint of the folded operculum is visible in the lower vesicle(Plate VIII, 3). It gives the original diameter of the aperture (53 µm) prior to the compression, which altered theA C C E P T E DM A N U S C R I P T

  Plate XII, 6; core 40, sample from 370.4 ft, IGR 72332 (Q48/2).

  Armoricochitina? sp.(Plate XIII, 2) possibly represents teratologic specimens (thickset vesicles) of A. gengi sp. nov.Other individuals, possibly belonging to this new species, are provisionally identified Armoricochitina cf. gengi sp. nov. (Plate XVII, 1-2) because the characteristic features, i.e.

Figs

  Figs.1a-c. Location map showing the study areas in Saudi Arabia (1a) and the position of the

Fig. 2 .

 2 Fig. 2. Lithostratigraphy, and Early Palaeozoic stratigraphic nomenclature in Saudi Arabia

Fig. 3 .Fig. 4 .

 34 Fig. 3. Lithological column and location of the studied core samples in the early Silurian

Fig. 12 . 6 . 2 . 3 , 9 .

 126239 Fig. 12. Cross plots of the measurements of Cyathochitina neolatipatagium sp. nov. Paris

Figure 1 A

 1 Figure 1

Figure 2 A

 2 Figure 2

Figure 6 A

 6 Figure 6

  Figure 14

  Figure 16

  Figure 21

  Figure 22

  Figure 24

  Conochitina alargada is moderately abundant (1% to 15%), except at 235.4 ft (35%) and in the upper part of the biozone where C. alargada represents less than Table19). Subordinate species are fairly rare (usually less than 3%) and long ranging taxa (Fig.6; Table19), as e.g. B. arabiensis, P. deichaii(Plate III,[START_REF]Three dimensional vesicle with the carina near the equator of the chamber and the small disc-like operculum[END_REF], Cutichitina minivelata sp. nov., Belonechitina paravitreaParis and Al-Hajri, 1995 (Plate III,

	5% of the recorded species. C. edjelensis (14% at 231.4 ft), and Plectochitina
	pseudoagglutinans (Plate III, 7-8; 39% at 238.2/6 ft and 38% at 217.2 ft) are the other most
	common components (Fig. 6;

3) and C. sp. aff. C. densa

(Plate III, 5)

. Another species, Cutichitina minivelata sp. nov.

(Plate III, 9)

, shows a fluctuating abundance, ranging from none at 238.2/6 ft to 12% at 225.5

  had already pointed out such abundant but sporadic occurrences of Cyathochitina species in Baltoscandia.

	Range. The first undisputable A. hemeri specimens are identified at 210.9 ft. Because the
	index species is too rare in this sample (0.2% of the recorded chitinozoans), and for practical
	reasons of identification, the base of the biozone is fixed at 204.35 ft. The species is well-
	represented from 176.05 ft to 132.05 ft (highest processed sample) in the Qusaiba-1 core hole
	and is abundant from 269.0 ft to 140.6 ft in the Baq'a-4 well (Fig. 7; Table 20). It must be
	stressed that a few A. macclurei precursors (Plate VII, 3) occur in the upper part of the hemeri

Table 20

 20

	). It

Age assignment. The camilleae subbiozone is tentatively attributed to the upper Aeronian-

	lowermost Telychian? because in the Baq'a-4 core hole the index species ranges in an interval
	situated between strata yielding graptolites firmly attributed to the convolutus Biozone (269.4
	ft) below and to the guerichi Biozone (135.55 ft) above the top. Less conclusive graptolites
	occurring at 218.55 ft to 268.90 ft are questionably referred to the convolutus Biozone
	(Zalasiewicz et al., 2007, fig. 6). The LAD of A. camilleae sp. nov. is located close to but
	below the FAD of Calpichitina densa regarded as a Telychian species in Baltoscandia (see
	discussion below for the macclurei Biozone).

Table 21 )

 21 . Some new species are restricted to the lower part, e.g. Fungochitina merrelli sp.

	nov. (Plate IX, 1, 3; Plate X, 5) and Ancyrochitina alhajrii sp. nov. (Plate X, 2, 4), when
	others are restricted to the upper part of the macclurei Biozone (Fig. 8), e.g. Armoricochitina
	crassicarinata sp. nov. (Plate XI, 2; Plate XII, 2, 6; Plate XIV, 7) and Armoricochitina? sp.
	(Plate XIII, 2). Except for A. alhajrii sp. nov. and A. crassicarinata sp. nov., which represent respectively 27% to 42%, and 1% to 24% of the identified taxa in the corresponding samples, the relative abundance of the other new species is less than 10%. Calpichitina densa (Plate VIII, 7; Plate XII, 8; Plate XIII, 3) ranges virtually through the entire macclurei Biozone and can be used as an alternative species for identifying this biozone. C. densa, however, has a very low relative abundance ranging from 1% to 4% (Figs. 7-8). In the Baq'a-4 core hole, Plectochitina alisawyiahensis sp. nov. has its FAD at 140.6 ft, exactly in the same sample as M A N U S C R I P T A. macclurei. The relative frequencies of this polymorphic species fluctuate greatly. The
	A C C E P T E D species is separated here from other very similar but ill-defined Plectochitina species, e.g., P.

  Spectacular forms with an unusually well-developed membrane joining the proximal part of the broken processes are tentatively identified as P. cf. alisawyiahensis(Plate XV, 6) and as Anthochitina? sp. A new species, Plectochitina jacquelineae sp. nov. is restricted to the sample at 306.0 ft (Fig.8; Table21), i.e. at the base of the obtusa Biozone as defined above.

longicornis is however used here. Plectochitina alisawyiahensis sp. nov. is still present in this biozone but its relative abundance is much lower (4 % or less) than in the underlying macclurei Biozone. The long ranging P. deichaii is again fairly abundant (15% at 250.5 ft) as well as other taxa, with sporadic occurrences, e.g. C. minivelata sp. nov. or A. gr. aculeata.

Other interesting species are recorded in the biozone, e.g. Plectochitina lucasi sp. nov.

(Plate XV, 3, 7)

, which is dominant in the lower part of the obtusa Biozone (see below the definition of the lucasi subbiozone) and Armoricochitina gengi sp. nov.

(Plate XV, 1)

, which represents only 3% of the chitinozoans recorded at 250.5 ft (Fig.

8

; Table

21

). A. gengi sp. nov. was reported as Armoricochitina n. sp. aff. panzuda (see

[START_REF] Paris | Final report on chitinozoans from well ALISAWYIAH EW-9[END_REF] pl. 2, fig. 3a-b)

in cuttings from well ISWH EW-9. In this well, it ranges from 3247 ft to 3568.6 ft (990 m to 1088 m)

  Plectochitina jacquelineae sp. nov. occurs with all the major components recovered from the upper part of the macclurei Biozone, i.e. the index species itself, A. gr. aculeata, T. obtusa, P. alisawyiahensis sp. nov., C. minivelata sp. nov. (dominant in the assemblage with 37% of the recorded individuals) and the youngest recorded C. densa and C.

  1 ft (1004 m) to 3509.6 ft (1070 m) from ISWH EW-9. In terms of graptolite zones, no direct calibration of the obtusa Biozone is presently available in Saudi Arabia or in other northern Gondwana regions (e.g. Algeria, Spain). Tentatively, a mid-to late Telychian age assignment is proposed here based on indirect evidence, as the obtusa Biozone is recorded above early Telychian strata and does not contain the Sheinwoodian chitinozoans known in other northern Gondwana localities (Fig.9).

	The Plectochitina jacquelineae sp. nov. subbiozone is restricted to core 34 (306.0 ft) in the
	Baq'a-3 core hole. This taxon ranges briefly in cuttings from 3299.7 ft to 3509.6 ft (1006 to

1070 m) and in core 1 (at 1093.5 m, i.e. 3586.7 ft) in the ISWH EW-9 well. Based on graptolite evidences (graptolites of the turriculatus s.l. Biozone recorded up to 303 ft in Baq'a-3;

Table 4 ;

 4 emend Paris et al., 1999 Material: 33 sorted specimens from core 26 in the Qusaiba-1 core hole but ca. 300 additional individuals in the remaining organic residue. Figs.10a-b) with L ranging in the measured specimens from ca. 310 µm (collarette missing) to 686.7 µm(Plate II, 4). The narrow chamber has gently tapering straight flanks(Plate II, 4) or a drawn out claviform profile(Plate II, 5). No flexure or shoulder is present at the junction between the chamber and the long cylindrical neck, flaring near the aperture. The average ratio of the vesicle length (L) on chamber diameter (Dp) is ca. 7.6, and may exceed 10 (e.g., paratype,Plate II, 4). The length of the chamber is close to the length of the neck. A long prosome, usually with numerous septa, is located deeply in the neck. The lower part of this prosome (likely more robust) is frequently less flattened than the remaining part of the neck.

	Type species: Conochitina claviformis Eisenack, 1931
	Conochitina viiuae sp. nov. Paris (Plate I, 2; Plate II, 4-5)

v. 1985 -Conochitina proboscifera Eisenack, 1937; Molyneux and Paris, pl. 14, figs. 1a-b.

Derivation of the name: this species is dedicated to Viiu Nestor for her outstanding investigations on the Silurian chitinozoans from the Baltic area.

Holotype: Plate II, 5, core 26, 245.8 ft, IGR 72256 (M44/4).

Type locality: Qusaiba-1 core hole, North Central Saudi Arabia.

Type stratum: Qusaiba Member of the Qalibah Formation; core 26, sample from 245.8 ft, mid-Aeronian Paratype:

Plate II, 4, core 26, 245.8 ft, IGR 72256 (O44/3)

. rounded margin; convex to truncate ogival bottom with a large protruding mucron.

Description:

The total length of this very long and slender chitinozoan (mean vesicle length: ca. 425 µm; length of the holotype: 522.6 µm) shows important variations (see

Table 4 :

 4 Biometric data (micrometers) for Conochitina viiuae sp. nov. Means are based on 15 partly flattened specimens from the Qusaiba-1 core hole, core 26, at 245.8 ft depth (raw data: between brackets; *correction factor: 0.8; ** correction factor: 0.7). This new species is a typical Conochitina according the emended definition of this genus given byParis et al. (1999). The specimen recorded at 251.1 ft (Plate I, 2) is totally compressed and thus its original diameter was ca. 41 µm (i.e. within the Dp range of the species; see Table4). The folded and tilted base obscures its mucron. . In spite there are no statistical data available for the total length of the Libyan form, it is included in the synonymy of C. viiuae, sp. nov. Conochitina alargada Cramer, 1967 has a stouter vesicle and no protruding mucron. Conochitina leptostoma Laufeld, 1974 from the early Wenlock of Gotland has also a slim vesicle, but its mucron is smaller and its flanks taper up to the aperture. Conochitina praeproboscifera Nestor, 1994 is wider (L/Dp ca.4-4.5) and Range and geographic distribution: In the Qusaiba-1 core hole, Conochitina viiuae sp. nov. has been recorded in core 26 (245.8 ft) where it represents 15% of the identified chitinozoans.

	Discussion:

Other very elongate Conochitina species (L/Dp > 6) have already been reported in the Ordovician and in the Silurian. Comparisons, however, are restricted here to Late Ordovician and to Silurian species. Conochitina incerta Eisenack, 1962 from the Late Ordovician of Baltoscandia has a sharper margin and a smaller mucron. Conochitina rotundata sp. nov. Paris et al. (this volume) from the late Katian of the Qusaiba-1 core hole has a sub-cylindrical vesicle and a base with a different shape (see discussion in Paris et al., this volume).

Conochitina proboscifera Eisenack, 1937 and even the "forma truncata" described by

[START_REF] Laufeld | Silurian Chitinozoa from Gotland[END_REF]

have much thicker walls and a less slender silhouette. In the Llandovery of well D1-31 in Cyrenaica (eastern Libya) Paris in

[START_REF] Molyneux | Palynostratigraphy of Northeast Libya[END_REF]

identified as C. proboscifera a chitinozoan with a silhouette and a mucron very close to those of C. viiuae sp. novhas a mucron less well-developed than C. viiuae sp. nov (L/Dp>6). Conochitina rara Nestor,

  Spinachitina sp. aff. maennili(Nestor, 1980b);Paris, pl. 2 fig. 7a-b. v. 1995 -Spinachitina maennili (Nestor, 1980b);Paris et al., fig. 2 p. 79.

	v. 1991 -Derivation of the name: This species is dedicated to Dr Geert Van Grootel who described this species in his doctoral thesis under the name Spinachitina spinosa sp. nov. Unfortunately this species remained unpublished and has to be considered as a nomen nudum (see discussion below). M A N U S C R I P T Holotype: Plate VII, 7, core 28, 240.7 ft, IGR 72371 (P42/4).
	A C C E P T E D
	Spinachitina geerti sp. nov. Paris (Plate VII, 1, 4-5, 7-8)
	? 1988 -Conochitina spp.; McClure, pl. VI, figs. 1-2 (non fig. 3).
	1990 -Spinachitina spinosa nomen nudum; Van Grootel, pl. 8, figs. 11-15.

emend Paris et al., 1999

Type species:

Conochitina cervicornis Eisenack, 1931 ? 1991 -Spinachitina bulmani Jansonius, 1964; Al-Hajri, pl. 25 figs; 1-4 (non figs. 5-6)

.

v. 1991 -Spinachitina maennili

(Nestor, 1980b)

; Paris, pl. 2 fig.

6a-b

. Type locality: Baq'a-4 core hole, North Central Saudi Arabia. Type stratum: Qusaiba Member of the Qalibah Formation; core 28, sample from 240.7 ft, Aeronian Paratypes: Plate VII, 1, core 28, 240.7 ft, IGR 72371 (Q42/1); Plate VII, 4, core 28, 240.7 ft, IGR 72371 (Q41/2); Plate VII, 8, core 28, 240.7 ft, IGR 72371 (Q41). Material: 25 sorted specimens (ca. 200 additional individuals in the remaining unpicked organic residue).

Table 5 :

 5 Biometric data (micrometers) for Spinachitina geerti sp. nov. Means are based on 15

		L	lp	Dp	dc	dcoll.	l. spines
	Holotype	231	171	(68.7)	(55.3)	(57.0)	6.7
				*55.0	**38.7	**40.0
	Mean	252	168	(82.4)	(54.6)	(58.3)	5.7
				*65.9	**38.2	**40.8
	Maximum	322	208	(101)	(65.3)	(65.3)	10.1
				*81	**45.7	**45.7

spinosa sp. nov. from the subsurface of the Brabant Massif (Belgium). Unfortunately this new species has not been published. According to the Zoological Code of Nomenclature it must be regarded as a nomen nudum. In his dissertation, Van Grootel gave an excellent description and provided a complete set of measurements of his new species. However, no SEM illustrations were provided and the reflected light microscope images

(Van Grootel, 199; pl. 8,

do not fully show the ornamentation. Consequently, for the stability of nomenclature it is preferred to designate another holotype from the present Saudi Arabian material and to leave "Spinachitina spinosa" as a nomen nudum. The specimens recorded by

Table 6 ;

 6 The lateral compression of the vesicle (flattening perpendicularly to the vesicle axis) generates radial folds of this carina (see left side of the carina on Plate VI, 7). Fig.12).

	Measurements (L	lc	Dp	Dc	l. carina
	Holotype	175	87	160.1	50	31
	Mean	199.6	94.3	167.6	61.8	22.7
	Maximum	284.8	154.1	237.9	83.8	43.6
	Minimum	134	40.2	117.3	39.6	10.1

Table 6 :

 6 Lazarus" distribution with more than 5 million years between their ranges. For that reason and based on the slight differences listed above this new species is proposed.McClure (1988, pl. VII, fig. 16) and[START_REF] Al-Hajri | Systematics and biostratigraphy of Middle Ordovician to Lower Silurian chitinozoans of the Arabian Peninsula[END_REF] illustrated Cyathochitina specimens with a large carina from the Qusaiba Member of the Qalibah Formation from the subsurface of the Tabuk and Qasim areas that most likely belong also to C. neolatipatagium sp. nov. (see synonymy list).

	Discussion: C. neolatipatagium sp. nov. is distinguished from most the other Cyathochitina
	species, except from C. latipatagium Jenkins, 1969, which also has a very wide carina. The
	carina of the latter, however, is thinner than the carina of C. neolatipatagium, which chamber

Biometric data (micrometers) for Cyathochitina neolatipatagium sp. nov. Means are based on 40 specimens from the Qusaiba-1 core hole, core 14 at 136.5 and 133.35 ft depth (no correction factor for compression used as most vesicles are three-dimensional; see Pl. 6).

has a thickened margin. The widest part of this chamber is located just above the carina. The two species are very similar, but it is unlikely that C. latipatagium specimens can have a

Table 7 :

 7 Biometric data (micrometers) for Ancyrochitina alhajrii sp. nov. Means are based on 37 compressed specimens from the Ba'qa-3 core hole, core 47 at 431.7 ft depth (raw data:

		L	Lc	Dp	Dc	Dcoll.	l. processes
	Holotype	117.3	63.7	(82.1)	(30.2)	(40.2)	46.9
				*65.7	**21.2	**28.2
	Mean	126.7	63.1	(79.5)	(33.1)	(42.3)	50.8
				*63.6	**23.2	**29.6

  distribution: A. alhajrii sp. nov. is only recorded in the Baq'a-3 core hole, in cores 47 to 42 (431.7 to 388 ft; Fig.8; Table21). It is the dominant species in three samples (e.g. 42% at 408.7 ft; see Fig.8; Table21) belonging to the Qusaiba Member of the Qalibah Formation. The corresponding interval corresponds to the lower part of the macclurei Angochitina camilleae nomen nudum;Paris, pl. 2, figs. 1 and 6.

	v. 2005-Derivation of the name: this species is dedicated to my granddaughter Camille Paris Holotype: Plate VIII, 1, core 19, at 163.0 ft, IGR 72364 (P41/4). Type locality: Baq'a-4 core hole, North Central Saudi Arabia. Type stratum: Qusaiba Member of the Qalibah Formation; core 19, sample from 163.0 ft, M A N U S C R I P T Aeronian.
	A C C E P T E D
	Biozone (merrelli and crassicarinata subbiozones pro-parte) and is assigned to the early
	Telychian (Figs. 8-9), based on graptolite evidence (turriculatus Biozone).
	Ancyrochitina camilleae sp. nov. Paris (Plate VIII, 1, 6)

Paratype: Plate VIII, 6, core 19, at 163.0 ft, IGR 72364 (P44).

Table 8 :

 8 Biometric data (micrometers) for Ancyrochitina camilleae sp. nov. Means are based on 30 compressed specimens from the Ba'qa-4 core hole, core 19 at 163.0 ft depth (raw data:

	between brackets; * correction factor: 0.8; **correction factor: 0.7; ***correction factor: 0.9.

Discussion: This new species is reminiscent of several other Late Ordovician or early Silurian

Table 10 :

 10 Biometric data (micrometers) for Plectochitina alnaimi sp. nov. Means are based on 55 compressed specimens from the Qusaiba-1 core hole, core 14 at 140.1 ft depth (raw data:

Table 11 :

 11 Biometric data (micrometers) for Plectochitina jacquelineae sp. nov. Means are based on 40 compressed specimens from the Baq'a-3 core hole, core 34 at 306.0 ft depth (raw

	L	Lc	Dp	Dc	Dcoll.	lproc.

data: between brackets; *correction factor: 0.8; ** correction factor: 0.7).

  R I P T processes (P. sp. aff. jiangsuensis inParis, 1993, pl. 2, figs. 6-7) have been reported from strata assigned here to the crassicarinata subbiozone. They are slightly different from P. jacquelineae sp. nov. and are not included in the synonymy. They may represent ancestors of this new species and only the youngest specimens (cuttings from 1006 to 1070 m) reported as P. jiangsuensis inParis (1993, fig. 2) are included in the synonymy. The very peculiar silhouette related to the occurrence of a crown of numerous processes is only reported in Ancyrochitina erichseni[START_REF] Sommer | Quitinozoários do furo 56, Itaituba, Pará[END_REF] In the Brazilian species, however, the processes are better developed and the ratio chamber length on the neck length is different. Plectochitina jiangsuensis described by[START_REF] Liang-Yu | Llandoverian Chitinozoa from Borehole DI-2 AT Dadua, Xinghua, Jiangsu[END_REF] from the Llandovery of China has a similar morphology but its processes are longer and joined at their distal end by a rim. Anthochitina primula Nestor, 1994 from the Llandovery of Estonia has a well-developed spiny neck and a membranous rim surrounding the margin.

Table 12 :

 12 Biometric data (micrometers) for Plectochitina lucasi sp. nov. Means are based on 36 compressed specimens from the Baq'a-3 core hole, core 30 at 271.8 ft depth (raw data: Discussion: Plectochitina lucasi sp. nov. is one of the numerous Plectochitina with multirooted processes. In the present case, however, the rooting is rather short and is different from the rooting of the processes of P. alisawyiahensis sp. nov. (see above). Ancyrochitina species with large hollow processes (e.g. A. fragilisEisenack, 1955a or A. magna Nestor, 1982) have Small Fungochitina species with a flat-based conical chamber and a short cylindrical neck; conspicuous flexure; rounded margin; well-developed simple or "lambdatype" spines randomly arrayed on the vesicle, but longer near the margin.

	between brackets; *correction factor: 0.8; ** correction factor: 0.7).

Diagnosis:

Table 13 :

 13 Biometric data (micrometers) for Fungochitina merrelli sp. nov. Means are based

	on 13 compressed specimens from the Baq'a-3 core hole, at 450.1 ft depth and 9 specimens
	from the Baq'a-4 core hole core at 120.1 and 40.1 ft (raw data: between brackets; *correction
	factor: 0.8 ; ** correction factor: 0.7).

-

  Sphaerochitina sp. indet.;Paris, fig. 6. v. 2005 -Muscochitina sp. nov. 1; Paris, pl. 6, figs. 1a-b, 4a-c.Derivation of the name:The species is dedicated to my son Olivier Chang Paris, for his help in preparing my photographic plates, drawings and databases.Type locality: Qusaiba-1 core hole, core 27, North Central Saudi Arabia. This medium sized Muscochitina species with a vesicle length (L) ranging from ca. 110 µm to 195 µm (L holotype: 147.4 µm; mean: 140.1 µm; seeTable 14, Figs. 20a

	Holotype: Plate I, 4, core 27, sample at 251.1 ft, IGR 72253, (O49).
	Type stratum: Qusaiba Member of the Qalibah Formation, core 27, 251.1 ft, mid Aeronian
	(upper part of the qusaibaensis Biozone)
	Paratype: Plate I, 1, core 27, sample at 251.1 ft, IGR 72253, (M44/1).
	Material: 58 picked specimens from the organic residue of Qusaiba-1 core 27 at 251.1 ft, and
	about 240 additional specimens in the remaining unpicked residue (see Table 1)
	Diagnosis: Muscochitina species with a flaring neck, well-differentiated from the ovoid to
	spherical chamber; vesicle covered with a mesh-like structure composed of thin threads
	radiating from dispersed short pillars or knobs.

Description:

Table 11 :

 11 Biometric data (micrometers) for Muscochitina olivieri sp. nov. Means are based on ornamentation of Muscochitina samiri[START_REF] Boumendjel | Nouvelles espèces de chitinozoaires du Silurien Supérieur et du Dévonien Inférieur du bassin de Timimoun (Sahara central, Algérie)[END_REF] is restricted to the margin and is not arranged in finial structures. When the finial ornamentation is eroded, M. olivieri sp. nov. may be confused with Sphaerochitina solitudinaParis, 1988b as only granules corresponding to the scars of the minute pillars are preserved on the wall surface (seePlate I, 6). Because the tiny threads of the finial structures, SEM observations are required for identifying this new species.Range and geographic distribution:In the Qusaiba-1 core hole, Muscochitina olivieri sp. nov. occurs in core 27, at 251.1 ft where it is abundant. Very rare specimens are also recorded in core 26 at 248.3 ft. The new species seems restricted to the upper part of the qusaibaensis chitinozoan biozone assigned to the mid Aeronian on graptolite evidence (convolutus Biozone; see discussion above). M. olivieri sp. nov. was also reported under the provisional name "Sphaerochitina sp. indet." from core 17, at 16635.7 ft depth in the UDYN-1 well

	37 compressed specimens from the Qusaiba-1 core hole, core 27 at 251.1 ft depth (raw data:
	between brackets; *correction factor: 0.8; ** correction factor: 0.7).
	Discussion: Muscochitina muscosa Paris, 1981 has a better-developed neck and its
	ornamentation is made of a regularly and densely meshed network. The mesh-like

  Type species: Desmochitina bursa Taugourdeau and de Jekhowsky, 1960 Plate VIII, 3, core 19, sample at 163.0 ft, upper vesicle, IGR 72364 (O46/1). Baq'a-4 core hole, core 19, north-western Central Saudi Arabia Type stratum: Qusaiba Member of the Qalibah Formation, core 19, sample at 163.0 ft, late Aeronian (upper part of the hemeri Biozone).

	Bursachitina baqaensis sp. nov. Paris (Plate VIII, 3)
	2005 -Bursachitina baqaensis nomen nudum; Paris, pl. 2, fig. 3.
	Derivation of the name: from the Baq'a locality in north-western Central Saudi Arabia, where
	the Baq'a-4 core hole was drilled.
	Type locality: Paratype: Plate VIII, 3, core 19, 163.0 ft, lower vesicle, IGR 72364 (O46/1).
	Material: 32 isolated vesicles and four connected vesicles (as two twins) from core 19, at
	163.0 ft in the Baq'a-4 core hole.
	Diagnosis: Bursachitina species with a distinct sharp margin; vesicle thick at margin and
	smooth; slightly convex base with a circular scar; thin collarette with finely serrate lips.
	Description: The observed vesicles are perfectly smooth (the granules on the lower specimen
	on Plate VIII, 3 are small mineral crystals that formed during the drying of the specimen). The
	vesicle is rather small (L ranging from ca. 74 µm to 164 µm; L holotype: 110.6 µm; Dp
	holotype near the margin: 97.2 µm) (Table 15;

Holotype:

Table 15 ;

 15 Figs.21a-b).

		L	lp	lcoll.	Dp	Dcoll.
	Holotype	110.6	83.8	24.5	(97.2)	(60.3)
					*77.8	**42.2
	Mean	113.6	85.1	30.0	(92.2)	(60.4)
					*73.8	**42.3
	Maximum	164.0	137.4	50.3	(120.6)	99.2
					*96.5	**69.5
	Minimum	73.7	57.0	10.1	(73.7)	(45.6)
					*59.0	**32.0

Table 15: Biometric data (micrometers) for Bursachitina baqaensis sp. nov. Means are based on 36 flattened specimens from the Ba'qa-4 core hole, core 19, at 163.0 ft depth (raw data: between brackets; *correction factor: 0.8; ** correction factor: 0.7).

Table 16 ;

 16 Figs.22a-b).

		L	Dp	l."sleeve"
	Holotype	33.5	57.0	6.7

Table 16 :

 16 Biometric data (micrometers) for Cutichitina minivelata sp. nov. Means are based on 53 compressed specimens from the Qusaiba-1 core hole, core 24 at 228.8 ft and core 14 at 136.5 ft depth (raw data: between brackets; *correction factor: 0.8).

  ). In all likelihood may be a C. minivelata sp. nov. compressed laterally as some spongy remains seem present on the flanks. The specimen tentatively referred to P. perivelata byMcClure (1988, pl. VI, fig. 8) is axially compressed and is surrounded by a spongy structure recalling that of C. minivelata sp. nov. Some specimens are puzzling such as the three vesicles illustrated on Plate IX, 5 and assigned to P. deichaii. They have a spongy surface but in transmitted light microscopy, a carina is visible on the lower vesicle, which shows in addition a short collarette around a narrow aperture.C. minivelata sp. nov. is abundant in core 17 from the UDYN-1 well and in cores 18-20 from TINT-2 well (see synonymy) where it was provisionally referred to Calpichitina cf. densa

	M A N U S C R I P T
	A C C E P T E D
	Cutichitina minivelata sp. nov. has been confused (see synonymy) with P. deichaii as their
	total-range overlaps. SEM observations prove that the specimens of P. deichaii (e. g., Plate II,
	3a-b; Plate XVI, 8) associated with C. minivelata sp. nov. in the Qusaiba-1 core hole have a

different flattening pattern, and display a disk-like aspect when flattened and even buckled

(Plate II,

. The specimen illustrated by

McClure (1988, pl. VI, fig. 13) as H. complanata

Table 17 :

 17 Biometric data (micrometers) for Armoricochitina crassicarinata sp. nov. Means are based on 45 compressed specimens from the Ba'qa-3 core hole, core 40 at 370.4 ft depth (raw data: between brackets; *correction factor: 0.8; ** correction factor: 0.7). This curving may modify significantly the outline of the vesicles (e.g., holotype on Plate XII, 2, versus paratype,Plate XII, 6). The resulting variable morphologies are regarded as simple intraspecific fluctuations as no trend through time is observed.Only a few other Armoricochitina have been described. Compared to A. crassicarinata sp. the subsurface of the Tabuk area (sample 9 from well "QA").Derivation of the name: this new species is dedicated to Professor Geng Liang-Yu (Nanjing, China) for his impressive work on the Silurian chitinozoans from China.

	nov., A. nigerica (Bouché, 1965) from the Late Ordovician of northern Gondwana has a
	better-developed membranous carina and bears small granules on its wall (see Paris et al., this
	volume). A. armoricana (Rauscher and Doubinger, 1967) is a Darriwilian species with a more

Discussion: As frequently observed in Armoricochitina species (e.g. A. nigerica; see

Paris et al., this volume)

, significant intraspecific morphological variations are noticed in the recovered populations of A. crassicarinata sp. nov. These variations concern mainly the length of the collarette (Fig.

23b

). They may also implicate the development of the carina (slightly longer or thinner in some specimens) and the degree of curving of the sigmoid flanks.

Type locality: Baq'a-3 core hole, core 27, at 250.5 ft, north-western Central Saudi Arabia Type stratum: Qusaiba Member of the Qalibah Formation, core 27, at 250.5 ft, Telychian (obtusa Biozone).

Table 18 ;

 18 Figs.24a-b).

		L	lcoll.	Dp	Dcoll.	l carina
	Holotype	140.7	73.7	(105.6)	(67.0)	16.8
				*84.5	**46.9
	Mean	142.1	69.5	(99.6)	(65.2)	13
				*79.7	**45.7
	Maximum	190.0	90.5	(118.9)	(77.1)	18.5
				*95.2	**54.0
	Minimum	90.5	43.6	(77.1)	(50.3)	6.7
				*61.7	**35.2

Table 18 :

 18 Biometric data (micrometers) for Armoricochitina gengi sp. nov. Means are based on 16 compressed specimens from the Ba'qa-3 core hole, core 27 at 250.5 ft depth (raw data:

Table 19 to Table 21. As a consequence, the former "Table 19" is transferred in a new Appendix D as Table

Plate XVIII

Acknowledgements

A C C E P T E D M A N U S C R I P T

The authors thank the Saudi Arabian Ministry of Petroleum and Mineral Resources and the Saudi Arabian Oil Company (Saudi Aramco) for granting permission to publish this paper.

They also thank very warmly Bernard Owens who initiated the very first steps of this CIMP/Aramco research project.

Olivier Chang Paris prepared the plates and the figures of this paper and organised the repository of the palynological slides and the loading of the relate material in databases.

The authors are grateful to the two reviewers, Antony Butcher (Portsmouth University, UK)

and Jacques Verniers, (Ghent University, Belgium), for valuable remarks and comments.

Plectochitina alnaimi sp. nov. Paris (Plate III, 6; Plate IV, 9; Plate V, 2, 10) 1991 pl. 30, fig. 5. 2005 -Ancyrochitina nov. sp. A; Paris, pl. 3, fig. 9; pl. 2, figs. 3 and 10. Derivation of the name: This new species is dedicated to Abdulla Al-Naim, the Vice President for Exploration in Saudi Aramco who has been an active supporter of the CIMP/Saudi Aramco project from its inception.

Holotype: Plate V, 2, core 14, sample from 140.10 ft; IGR 72291 (Q42).

Type locality: Qusaiba-1 core hole, North Central Saudi Arabia.

Type stratum: Qusaiba Member of the Qalibah Formation; core 14, sample from 140.1 ft, Aeronian.

Paratype: Plate V, 10, core 16, sample from 150.8 ft, IGR 72286 (R44).

Material: 2178 specimens picked from cores 27 to 32 (136.5 to 217.2 ft depth) from the Qusaiba-1 core hole (Fig. 6) and several thousand additional specimens in the corresponding unpicked residue (Table 1).

Diagnosis: Small Plectochitina species with a conical chamber and a short cylindrical neck (L/lc close to 2) ended by a flaring collarette; granules or blunt cones cover the vesicle wall; up to eight bi-or more rarely multi-rooted processes with a spongy to cell-like (vesicular) internal structure.

Description: This chitinozoan is quite small: its vesicle length (L) ranges from ca. 74 to 134 µm, with an average length of ca. 110 µm. The holotype (L=103.9 µm) is shorter because the lips are partly folded within the aperture (Plate V, 2). The straight flanks (no shoulder observed) taper rapidly toward a conspicuous flexure. This gives a thickset aspect to the Subfamily Angochitininae Paris, 1981 Genus Fungochitina Taugourdeau, 1966 Type species: Conochitina fungiformis Eisenack, 1931. Fungochitina merrelli sp. nov. Paris (Plate IX, 1, 3; Plate X, 5) ? 1988 -Sphaerochitina lepta Jenkins, 1970; McClure, pl. VIII, figs. 11-12. ? 1991 -Ancyochitina merga Jenkins, 1970; Al-Hajri, pl. 30, figs.1-2, 4. 2005 -Angochitina milleri n. sp. nomen nudum; Paris, pl. 3, figs. 1, 3; pl. 4, figs. 5a-b. Derivation of the name: The new specie is dedicated to Mr Merrell Miller for his long collaboration and his extensive studies on the Saudi Arabian palynomorphs. Holotype: Plate IX, 1, core 49, sample from 450.1 ft, IGR 72340 (R45). Type locality: Baq'a-3 core hole, North Central Saudi Arabia. Type stratum: Qusaiba Member of the Qalibah Formation; core 49, sample from 450.1 ft, early Telychian. Paratypes: Plate IX, 3, core 49, sample from 450.1 ft, IGR 72340 (S45/3); Plate X, 5, core 9, sample from 450.1 ft, IGR 72340 (Q45/4).

Material: 13 specimens picked in the organic residues from cores 7 and 15 in the Baq'a-4 core hole (about 120 specimens in the remaining unpicked residues; see Table 2). 13 specimens picked in the organic residues from cores 47 to 49 in the Baq'a-3 core hole (about

Appendix B. Systematic palaeontology (F. Paris)

The classification and the terminology proposed by Paris et al. (1999) are used for the description of the new chitinozoan species defined in the Systematic section. The measurements of the morphological parameters are expressed in micrometres (µm) and the abbreviations defined by [START_REF] Paris | Les chitinozoaires dans le Paléozoïque du sud-ouest de l'Europe (Cadre géologique -Etude systématique -Biostratigraphie)[END_REF] are used i.e., total length (L), chamber diameter (Dp), neck diameter (dc), collarette diameter (dcoll.), collarette length (lcoll.), neck length (lc).

Biometric graphs give the size variations for each of the new species. The choice of holotypes with measurements close to the average values of the measured populations is favoured (Figs. [10][START_REF]Three dimensional vesicle with the carina near the equator of the chamber and the small disc-like operculum[END_REF][12][START_REF] Belonechitina | [END_REF][14][15][16][17][18][19][20][21][22][23][24]. For the measurements, a correction of the compression of the vesicle is used depending on the importance of the flattening, e.g. coefficient of 0.8 for the chamber (usually less affected because its thicker wall near the margin) and coefficient of 0.7 for the neck and the collarette (thinner wall and thus frequently totally compressed).

The sorted specimens and the individuals observed under a Scanning Electron Microscope (SEM) are housed in the palynological collections of the Geological department of Rennes University, France (Géosciences, OSUR), with the repository numbers IGR 72251 to 72376.

The coordinates of illustrated specimens are given using the England-Finder Grid.

Incertae sedis Group Chitinozoa [START_REF] Eisenack | Neue Mikrofossilien des baltischen Silurs I[END_REF] Order Prosomatifera [START_REF] Eisenack | Chitinozoen und andere Mikrofossilien aus der Bohrung Leba[END_REF] Family Conochitinidae [START_REF] Eisenack | Neue Mikrofossilien des baltischen Silurs I[END_REF], emend Paris, 1981

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frequently longitudinal cracks near the connection of these processes on the margin. These cracks to some extent may mirror the rooting of P. lucasi sp. nov. Among the long-necked Silurian Plectochitina species, P. clathrospinosa [START_REF] Eisenack | Microfossilien eines Geschiebes der Borkholmer Stufe, baltisches Ordovicium, F2. Mitt[END_REF]) has wide multi-rooted processes with very short and thin distal part (an assignment to Plectochitina is preferred here for this species; see Table 22). The general outline of the vesicle of A. parafragilis Al-Hajri and Paris, 1998 from the Sharawra Member is similar to that of A. lucasi sp. nov. but its chamber is more pear-shaped and its robust hollow processes have no multi-rooted proximal attachment, nor a cell-like internal structure. A. alhajrii sp. nov. is different in that it has processes without a spongy or vesicular internal structure.

In the upper part of the Baq'a-3 core hole, fairly long-necked chitinozoans have a silhouette similar to that of P. lucasi sp. nov. They are identified Plectochitina cf. lucasi and are differentiated from P. lucasi sp. nov. by their short and slender multi-rooted processes (Plate XVIII,1b,2b). Moreover, granules or cones are present on their chamber and neck (Plate XVIII,1a,1b).

Range and geographic distribution: P. lucasi sp. nov. is abundant in the Baq'a-3 well from 250.5 to 289.1 ft (cores 27 to 32). It is the dominant species at 271.8 ft (63% of the recorded chitinozoans; see Fig. 8). P. lucasi sp. nov. is the index species of the eponymous subbiozone.

This lucasi subbiozone is representative of the lower part of the obtusa Biozone referred to the Telychian (likely mid-to late Telychian; see stratigraphic discussion above, and Fig. 9).

Identical chitinozoan specimens were recorded in the ISWH EW-9 well, in cutting samples from 3478 ft to 3596.3 ft (1058 m to 1094 m) [START_REF] Paris | Final report on chitinozoans from well ALISAWYIAH EW-9[END_REF]pl. 2, figs. 1-2). These specimens provisionally called Ancyrochitina n. sp. B by [START_REF] Paris | Final report on chitinozoans from well ALISAWYIAH EW-9[END_REF] are included in the synonymy list of P. lucasi sp. nov. The corresponding samples from the ISWH EW-9 well are assigned to the lucasi subbiozone and are therefore of Telychian age (Fig. 9).

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Discussion: The length of the chamber (lp: vesicle length minus the well-developed collarette)

of this new species is close to its width (mean ratio lp/Dp: 0.92 but approximately 1.15 when the flattening is corrected; see Table 15 and Fig. 21b). This leads to its assignment to the genus Bursachitina as Euconochitina has a lp/Dp ratio exceeding one. Only a few specimens with an unusually short collarette with regard to the chamber length have been recorded (see Fig. 21b). B. pachygaster (Taugourdeau, 1963) Material: Several hundred vesicles, mostly in chain-like structures with up to fifty connected vesicles in cores 14 to 27 from the Qusaiba-1 core hole (Fig. 6; Table 19) and in cores 21 to 40 from the Baq'a-3 core hole (Fig. 8; Table 21); several hundred additional specimens, mostly in chain-like structures, were recorded in the TINT-2 and UDYN-1 wells.

Diagnosis: Small lenticular to thickset barrel-like vesicle without neck or collarette; felt-like to spongy membrane (velum) encapsulating the chamber; wide aperture with flat operculum; chain-like structure with resistant inter-vesicle connections.

Description: This very small chitinozoan (mean vesicle length close to 63 µm) has a lenticular chamber with rounded flanks and rather flat apertural and antiapertural surfaces. It usually

A C C E P T E D M A N U S C R I P T

slender vesicle and a better developed carina. A. ceneratiensis [START_REF] Paris | Les Chitinozoaires[END_REF] from the Lower Devonian of Brittany has a more ovoid chamber and smooth walls.

In the Baq'a-3 well, a few specimens with a long neck/collarette are provisionally referred to A. cf. crassicarinata sp. nov. (Plate XIII,7) as they may be end members of a polymorphic population (Figs. 23a-b). To some extents, the silhouette of A. cf. crassicarinata sp. nov.

(Plate XIII, 7) is reminiscent of those of A. armoricana [START_REF] Rauscher | Associations de Chitinozoaires de Normandie et comparaisons avec les faunes déjà décrites[END_REF] or of A. granulifera [START_REF] Nõlvak | Ordovician chitinozoan zones from Baltoscandia[END_REF]. A. crassicarinata sp. nov. is distinguished from A.

gengi sp. nov. by its thick rim-like carina (see discussion of A. gengi sp. nov. below).

Some Armoricochitina illustrated by Al-Hajri (1991, pl. 26, figs. 1-2, 4) from the Tabuk area (sample 9 from well "QA") have a short and fairly thick carina similar to that of A. crassicarinata sp. nov. They are therefore tentatively included in its synonymy list (see above).

Range and geographic distribution: A. crassicarinata sp. nov. may be abundant in the Qusaiba Member of the Qalibah Formation in the Baq'a-3 core hole (24% of the recorded chitinozoans at 350.1 ft; Fig. 8). In this well it ranges at least over 78.3 ft (23.8 m) from core 36 to core 45 and likely more as there is ca. 23 ft (7 m) separating these cores from the closest ones devoid of A. crassicarinata sp. nov. (Fig. 8; Table 21). This new species is selected as the index species of a subbiozone characterizing the upper part of the macclurei Biozone. This crassicarinata subbiozone is assigned to the early Telychian as the corresponding strata yield graptolites of the turriculatus Biozone (Fig. 9; see discussion above).

If one accepts the synonymy proposed here, A. crassicarinata sp. nov. occurs in cutting samples of the ISWH EW. 9 well from 3517.4 ft to 3602.9 ft (1070 m to 1096 m) [START_REF] Paris | Final report on chitinozoans from well ALISAWYIAH EW-9[END_REF]. In this well, it is the dominating species in the core samples at 3594.7 ft to 3609.5 ft.

(1093.5 m to 1098 m), which therefore have an early Telychian age.

The new species is probably also present in the Qusaiba Member of the Qalibah Formation in

where it is more common (Fig. 8; Table 21). The species ranges through the obtusa and the silurica biozones, which are referred to the Telychian (see Fig. 9 and the stratigraphical discussion above).

A. gengi sp nov. is very rare and irregularly represented in the ISWH EW-9 well. It was provisionally called "Armoricochitina n. sp. aff. panzuda" (see synonymy) and occurs in cutting samples from 3254.5 ft to 3576.6 ft (990 m to 1088 m ) [START_REF] Paris | Final report on chitinozoans from well ALISAWYIAH EW-9[END_REF]. 22. 22. Fig. 9. Chitinozoan biozones and subbiozones identified in the Qusaiba-1, Baq'a-4 and Baq'a-3 core holes. Correlation with the ISWH EW-9, and age assignments with regard to the early Silurian graptolite zonation [START_REF] Zalasiewicz | Early Silurian (Llandovery) graptolites from Central Saudi Arabia: first documented record of Telychian faunas from the Arabian Peninsula[END_REF][START_REF] Zalasiewicz | Graptolites in British stratigraphy[END_REF] and to the standard Silurian chronostratigraphy with the same colour code as in Figures 678.