Middle Permian ostracods (Crustacea) from the Guadalupe Mountains, West Texas, USA

Middle Permian (Guadalupian) ostracods are described from the Williams Ranch Member of the Cutoff Formation (Roadian) and the McKittrick Canyon Member of the Bell Canyon Formation (Capitanian) from two sections exposed in Culberson County, Guadalupe Mountains, West Texas. Their taxonomy is discussed and adds to the scientific understanding of marine ostracod biodiversity and palaeobiogeography during the Middle Permian. Ostracod assemblages are represented by 51 species of 26 genera and 15 families. Eleven species are newly described: Healdia mckittrickensis Crasquin sp. nov., Healdia cutoffella Crasquin sp. nov., Aurikirkbya guadalupensis Crasquin sp. nov., Hollinella (Hollinella) williamsranchensis Crasquin sp. nov., Geisina culbersonensis Crasquin sp. nov., Paraparchites pecosensis Crasquin sp. nov., Bairdia elcapitanensis Forel sp. nov., Ceratobairdia mescaleroella Forel sp. nov., Ceratobairdia sexagintaduella Forel sp. nov., Ceratobairdia pratti Forel sp. nov., and Denticupachydomella bellcanyonensis Forel sp. nov. The diagnosis of the genus Denticupachydomella is emended. The palaeobiogeographic distribution of the species is analyzed and exemplifies the taxon exchanges between Tethyan and Panthalassic localities in the Permian. The eastern margin of the Palaeo-Tethyan realm is shown to have played a major role in radiation of taxa in the Permian.


Introduction
The Guadalupian Epoch, Middle Permian, witnessed major global changes, including the formation of the Pangaea supercontinent, the end of the Late Palaeozoic Ice Age, and sea-level changes as well as major biotic events (e.g., Shen et al. 2020 and references therein). Ostracods are millimetre-size crustaceans that are significant components of the meiofauna known from the Early Palaeozoic (e.g., Salas et al. 2007) to the present time. It is now acknowledged that Permian marine ostracod communities went through significant changes up to the end-Permian extinction (see Forel 2014 andCrasquin 2020 for reviews) but their response to the so-called end-Guadalupian mass extinction remains enigmatic. The evolution of meiobenthic biodiversity through this key interval can only be understood by first characterizing the taxonomic structure of Middle Permian communities worldwide. Guadalupian marine ostracods have been reported, for instance, from Greece (Crasquin-Soleau & Baud 1998), Turkey (Kozur et al. 2000;Crasquin-Soleau et al. 2004), Sultanate of Oman (Crasquin-Soleau et al. 1999), the Russian Platform and Far East in Russia (e.g., Khivintseva 1969;Gramm 1997), Thailand (e.g., Chitnarin et al. 2012Chitnarin et al. , 2017, China (Zazzali et al. 2015), Japan (Ishizaki 1964;Tanaka et al. 2013), Afghanistan (Forel 2018), and North America (e.g., Girty 1908Girty , 1910Sohn 1954Sohn , 1960Sohn , 1982. In North America, Middle Permian ostracods have been described from the Guadalupian outcrops that are widespread in the Delaware Basin: in the Guadalupe, Apache and Glass mountains (Fig. 1). The Guadalupe Mountains are the World stratotype area for the Middle Permian and the Guadalupe Mountains National Park contains the GSSPs for the Roadian, Wordian and Capitanian stages (Glenister et al. 1999). The first appearance of the conodonts Jinogondolella nankingensis (Jin, 1960), J. aserrata (Clark & Behnken, 1979) and J. postserrata (Behnken, 1975), respectively, define the lower boundary of the Roadian, Wordian and Capitanian stages. The Guadalupian strata present in the Delaware Basin represent various palaeoenvironments from back reef, reef, fore reef to basinal.
The ostracods from the Delaware Basin are known from the Guadalupe and Glass Mountains. In the Guadalupe Mountains, the first ostracods were mentioned by Girty (1908) who described and illustrated (drawings) three species of silicified ostracods: Cythere? sp. from the "dark limestone" of Pine Spring ( = Goat Seep Limestone), Bairdia aff. plebeia Reuss, 1854 from basal black limestone ( = Bone Spring Limestone of King that includes members of the Cutoff Formation, Lambert et al. 2000) of Guadalupe Point, both from the Guadalupe Mountains, and Argilloecia sp. from the Delaware Mountain Formation of the southern Delaware Mountains. Sohn (1954) included Girty's species Argilloecia sp. in his species Miltonella shupei Sohn, 1950 andreillustrated it in Sohn (1954: pl. 5 fig. 19). Later, Sohn (1960: pl. 1 fig. 22) reillustrated another of Girty's species, Bairdia aff. plebeia, and assigned it to the species Bairdia pecosensis . According to Sohn (1982: 105), the third of Girty's species Cythere? sp. is "an unidentifiable broken smooth valve on limestone." Sohn (1961a) listed 23 species of ostracods from the Getaway Limestone Member of the Cherry Canyon Formation in the Guadalupe Mountains. Almost all species were identified in open nomenclature, except for six: Amphissites aff. centronotus (Ulrich & Bassler, 1906), Aurikirkbya aff. wordensis , Ceratobairdia wordensis , Healdia? vidriensis , Polytylites digitatus? Sohn, 1954, and Roundyella dorsopapillosa? Sohn, 1954 In the Glass Mountains, Guadalupian age ostracods have been studied from the Word # 1 limestone of the Word Formation ). According to Cooper & Grant (1964), this limestone is assigned to the Road Canyon Formation, which is of Roadian age (Wardlaw 2002). Also, ostracods have been described by Sohn (1950Sohn ( , 1954Sohn ( , 1962 from the upper part of the Leonardian or lower part of the Word Formation (USNM 703c locality that is assigned to the Road Canyon Formation) and the Road Canyon Formation (Sohn 1972).  and Sohn (1950Sohn ( , 1954Sohn ( , 1962 described 29 new species, some of which occur in the material studied herein. Herein, we analyse ostracod assemblages obtained from two sections in the Guadalupe Mountains area of West Texas: the Quarry section exposing the upper part of the Cutoff Formation (Roadian) and the MKCS1 section exposing the middle part of the Bell Canyon Formation (Capitanian). Ostracods are described and taxonomy is discussed, adding important information to better constraint the Middle Permian biodiversity of ostracod assemblages along the eastern Panthalassa margin. The palaeogeographical links with coeval assemblages are also analysed and provide evidence of Tethyan-Panthalassic exchanges through the Permian.

Geological setting
The Guadalupian strata of basinal setting exposed in the Delaware Basin are subdivided into the Cutoff, Brushy Canyon, Cherry Canyon and Bell Canyon Formations (Fig. 2).

Cutoff Formation
The history and stratigraphical nomenclature of the Cutoff Formation in the Guadalupe Mountains is discussed in Harris (2000), Lambert et al. (2000), Hurd et al. (2018), . The Cutoff Formation is a succession of alternating carbonate and siliciclastic rocks and recently has been subdivided into 5 members (Hurd et al. 2016(Hurd et al. , 2018: Shumard, El Centro, Butterfield, Rest Area, and Williams Ranch, in ascending order (Fig. 2). The lower boundary of the Roadian is in the middle of the El Centro Member as shown by the first appearance of the conodont J. nankingensis (Glenister et al. 1999;Lambert et al. 2000). The Williams Ranch Member is the uppermost member of the Cutoff Formation that unconformably overlies the Rest Area Member and is unconformably overlain by the Brushy Canyon Formation (Hurd et al. 2018). It ranges from 10 to 47 m in thickness and consists of deformed soft-sediments, thin-bedded carbonate mudstone, wackstone and packstone.
The Williams Ranch Member recently has been restudied and resampled by  for the radiolarian analysis in the Quarry section. Besides radiolarians, the studied samples contain conodonts, foraminifers, fish teeth and ostracods, the latter are investigated herein. The Quarry section is located along US Highway 62/180 3 km northeast of its junction with Texas Highway 54 (Fig. 3). The strata of the Williams Ranch Member of the Cutoff Formation are exposed as two roadcuts on both sides of the U.S. Highway 62/180. The ostracod fauna is studied from samples taken on the northwestern side of the highway in a small quarry that exposes about 13 m of limestone beds . The bottom of the section is composed of thin-bedded black carbonate mudstone with small black pebbles of packstone with soft-sediment deformation. A zone of debris with exposures in some places of thin-to medium-bedded black carbonate mudstone with lenses of mollusc-bearing packstone occur higher in the section. The packstone lenses contain ammonoids, a very rich assemblage of fish remains, small foraminifers, rare fusulinids, conodonts, diverse radiolarians, scolecodonts, holothurian sclerites, and ostracods (Spinosa et al. 1975;Lambert et al. 2000;Nestell et al. 2015;.

Bell Canyon Formation
In the Guadalupe Mountains, the Bell Canyon Formation is subdivided into seven limestone members (in ascending order): Hegler, Pinery, Rader, McCombs, 'McKittrick Canyon' (its status is not formalised yet), Lamar and Reef Trail (Fig. 2). The ostracods were studied from the 'McKittrick Canyon' Member exposed in one section (MKSC1) at the locality GUMO GEO 00252 in the Patterson Hills area (Ivanov et al. 2020). Strata of this locality are represented by thin-bedded limestone about 3 m thick with several thin beds of debris flow. Eight samples were taken from this locality, but ostracods have been found only in two samples. It is worthy to note that fish remains have recently been described from this locality (Ivanov et al. 2020). ). The orange area shows the Park and its boundary. The section MKSC1 is located within the park but its precise position cannot be disclosed because of park regulations.  -Bradley, 1961Suborder Metacopina Sylvester-Bradley, 1961 Superfamily Healdioidea Harlton, 1933Family Healdiidae Harlton, 1933 Genus  (Ulrich & Bassler, 1906 RV with Hmax at mid-L; AB with maximum of convexity located slightly below Hmax; VB slightly concave at both valves; PB large and close to vertical; presence of two posterior spines quite large, their bases are linked by an intra-spines tenuous ridge; in front of the spines, presence of a curved ridge, more developed than the intra-spines one; surface smooth.

Diagnosis
A species of Healdia with a short and stocky carapace and a posterior ridge more or less vertical without spines, ADB longer than PDB in both valves.

Etymology
After the Cutoff Formation, Roadian, Middle Permian, West Texas that contains this species.

Description
Short and stocky carapace, egg-shaped in lateral view; LV strongly overlaps RV all around the carapace; ADB longer than PDB at both valves; AB large with maximum of curvature located around mid-H; PB quite equivalent to AB; presence of a posterior vertical to slightly tilted ridge, without spines; carapace laterally compressed posterior to ridge, more strongly at LV.

Remarks
Healdia cutoffella sp. nov. is very similar to Healdia simplissima Harlton, 1933 from the Pennsylvanian of Texas and Oklahoma (Harlton 1933;Hoare & Merrill 2004). Both species have the same ridge without spines, equivalent AB and PB, but mainly differ by PB being longer than AB in H. simplissima (herein AB is longer than PB).

Remarks
This specimen shows a clear oval kirkbyan pit in the middle part of the valve. The right valve has PB and AB with a different radius of curvature, whereas they are quite equivalent in Kirkbyidae. Herein, the PB has a very small radius of curvature and AB a large one. The ornamentation is coarse.

Remarks
The specimens have a transitional morphology between Kindlella Sohn, 1954 andKellettina Swartz, 1936. They have the carapace outline and characters of Kindlella and lobes overpassing the DB as in Kelletina.

Remarks
The general outline of Kirkbya sp. is close to that of Kirkbya permiana (Jones, 1850) in Woszczyńska, 1987 from the Late Permian of Poland (Woszczyńska 1987) and to Kirkbya bendensis Harlton, 1933 from the Pennsylvanian of USA (Harlton 1933) but the ornamentation in the Texan specimens is very different by a very fine reticulation.

Diagnosis
A species of Aurikirkbya with an additional ventral ridge parallel to the adventral ridge, extending from mid-H in the anterior part to mid-H in the posterior part of the carapace.

Etymology
After the Guadalupe Mountains, West Texas, USA, where this species has been discovered.

Description
Carapace sub-rectangular in lateral view with Hmax located in anterior half; Lmax located in dorsal part of Hmax; DB long and straight; posterior shoulder clearly expressed, ACA close to 90° or slightly obtuse; PCA close to 90° or slightly acute; AB with large radius of curvature with maximum located around mid-H; VB almost straight with weak median concavity, parallel to DB; PB with small radius of curvature and maximum located close to DB; 2 vertical lobes connected above kirkbyan pit by small sub-horizontal lobe; kirkbyan pit located at mid-L and below mid-H; two important ridges along free margins, one ventral and one adventral; marginal structure underlined by tubercles; adventral ridge smooth as well as areas around cardinal angles; additional ridge parallel to adventral one, extending from mid-H in anterior part up to mid-H in posterior part of the carapace; presence of a dorsal shield characteristic of the genus; surface reticulate.

Remarks
Aurikirkbya guadalupensis sp. nov. differs from the three species described by Sohn (1950) (A. wordensis , A. barbarae Sohn, 1950 andA. auriformis Sohn, 1950) from the Roadian (upper Leonardian or lower Wordian in the sense of Sohn 1950) of the Glass Mountains, Texas by a smaller PB and a diagnostic ridge. Aurikirkbya kelletae (Harlton, 1929) from the Pennsylvanian of Texas and Aurikirkbya miyakei Yanaka & Ono in Tanaka et al., 2012 from the Early Permian of Japan (Tanaka et al. 2012) have a similar carapace shape but differ by the diagnostic ridge.  Fig

Remarks
This specimen could belong to a new species with regard to the ornamentation of the carapace that consists of small ridges on the anterior part and a reticulation on the posterior part. The general shape is similar to that of Kirkbyella (Berdanella) quadrata Croneis & Gutke, 1939 sensu Hoare & Mapes 2000 from the Mississippian of Arkansas (Hoare & Mapes 2000) but in this species the reticulation is organised quite horizontally and here it is more oblique.

Description
Carapace auriform and elongate in lateral view; Hmax at ACA; Lmax at mid-L; DB long and straight; presence of cardinal spine at PCA; AB with maximum of curvature at or below mid-H; VB straight; PB with quite large radius of curvature underlined by nodules; presence of a granular velum that ends by posterior spine; L 1 well expressed, vertical and in continuation of ventral lobe, ended dorsally by small nodule/spine; L 2 well expressed, peaked, with small nodule; L 3 covered by nodules, higher than DB; surface granular; intraspecific variations observed in velum formed by small spines (Fig. 6L) and blade (Fig. 6I). Superfamily Kloedenelloidea Ulrich & Bassler, 1908 Family Glyptopleuridae Girty, 1910 Genus Glyptopleura Girty, 1910 Type species

Remarks
A species of Glyptopleura with 6 thick ridges on the lateral surface, the upper two ridges are shorter than the others and end before PB. This species may be new, but the material is poorly preserved. So far, this species is the youngest representative of Glyptopleura.

Description
Carapace sub-rectangular in lateral view with Hmax in anterior ⅓ rd of L and Lmax slightly below mid-H; DB long and straight; ACA = 115°-130°, PCA = 105°-115°; AB with large radius of curvature with maximum at lower ⅓ rd H; VB nearly straight; PB laterally compressed, large with maximum of curvature located at mid-H; free margins bordered by small spines; L 2 not well visible; S 2 round and clearly marked; L 3 underlined by two large spines, one dorsal and one medio-ventral, pointing upward; surface completely covered with pustules.

Remarks
Geisina culbersonensis sp. nov. has a very particular shape and primary ornamentation. It can be compared with Geisina sp. in Chitnarin et al. 2012 from the Asselian-Sakmarian, Early Permian of Thailand (Chitnarin et al. 2012), which has a smaller PB and a smooth surface.

Remarks
This species is similar to Miltonella shupei Sohn, 1950 from the Middle Permian of Texas (Sohn 1950). Herein, the specimens are shorter and the characteristic ridge of the genus begins at ACA and finishes at PCA (instead of PB in type species).

Remarks
The specimen is similar to Libumella athabascensis Green, 1963 from the Mississippian of the Rocky Mountains, Canada (Green 1963;Crasquin 1985) and from the Late Permian of South China (Yuan et al. 2007). Nevertheless, it differs by the presence of a nodule in the dorso-median part of the carapace.

Etymology
In reference to the Pecos River, West Texas, USA.

Remarks
Paraparchites pecosensis sp. nov. has a lateral outline similar to that of Paraparchites texanus Ulrich & Bassler, 1906emend. Scott, 1959 from the Early Permian of Texas . The main difference between the two species is the small hemi-circular ridge at PB in the new species.

Preliminary remarks
The classification of ornate Bairdiidae is complex and still disputed mainly because of the difficulty to unravel the taxonomic significance of their lateral ornamentation features. As detailed in Forel & Grădinaru (2020), the revision of their classification requires the addition of new characters to avoid producing another classification system that would only be a new point of view further complicating the current situation. The peak of diversity of ornate Bairdiidae occurred in the Late Triassic but they were already present in the Permian (see Forel & Crasquin 2020 and references therein for a review) as illustrated for instance by the material described herein from the Middle Permian of the Guadalupe Mountains. Specifically, the confusion and instability of the conceptions of Petasobairdia Chen, 1982 and Praelobobairdia Kozur, 1991 have recently been described and discussed in Forel & Grădinaru (2020). Herein, we follow the view that Praelobobairdia is a junior synonym of Petasobairdia, as was first introduced by Becker (2001).

Diagnosis
A species of Bairdia with asymmetric valves and with a strong overlap along DB; ADB concave at RV and dorsal margin uniformly convex; PD and AD angles laterally compressed at RV.

Etymology
In reference to the El Capitan Peak located within the Guadalupe Mountains National Park, Guadalupe Mountains, West Texas, USA.

Description
Carapace sub-triangular in lateral view with asymmetric valves and overlap of LV all around RV with maximum along DB; lateral surface smooth. LV: Hmax around mid-L; dorsal margin uniformly convex with PDB and ADB almost straight; AB with small radius of curvature located above mid-H; VB straight to only gently concave; PB narrow with maximum of convexity located very ventrally. RV: Hmax located at AD angulation; DB long and straight, gently bent posteriorly; PDB straight with terminal concavity; ADB concave; PD angle (130-135°) and AD angle (135-140°) laterally compressed; AB with relatively small radius of curvature, located above mid-H; oral concavity in front of mid-L at ventral margin; PB slighted.

Remarks
Bairdia girtyi Sohn, 1960sensu Hoare & Merrill, 2004 from the Pennsylvanian of Texas (Hoare & Merrill 2004) is similar to Bairdia elcapitanensis sp. nov. by its lateral morphology, but lacks the AD and PD angulations at RV. It is worth noting that the specimens of Hoare & Merrill (2004) do not belong to Bairdia girtyi Sohn, 1960 from the Late Mississippian of USA (Sohn 1960), because Bairdia girtyi is more elongate, with PB located higher and Hmax located slightly behind mid-H.

Diagnosis
A species of Ceratobairdia with three spines, two long and one short, along the dorsal margin of LV and the ventro-lateral ala not terminated by spine.

Etymology
From the tribe of Mescalero Apaches who inhabited parts of the Southwest US and Northwest Mexico.

Material examined
Holotype USA • left valve, (Fig. 8O) Sohn, 1954 from the Roadian, Middle Permian of Texas (Sohn 1954) is morphologically very similar to Ceratobairdia mescaleroella sp. nov., but the new species differs by its relatively smaller dimensions, three thicker dorsal spines, lack of a terminal sharp spine at the latero-ventral ridge and PB located higher and more upturned. Sohn (1954) observed that specimens of Ceratobairdia dorsospinosa Sohn, 1954 have one or two spines along the dorsal margin of LV. However, all other characters of the carapaces and valves are very similar, so he suggested that all specimens are conspecific. Although very similar morphologically, Ceratobairdia mescaleroella sp. nov. cannot be considered as another degree in the variability of Ceratobairdia dorsospinosa Sohn, 1954 as the lateral morphologies of the two species are significantly different as detailed above. Contrary to what was shown for Ceratobairdia dorsospinosa Sohn, 1954, Ceratobairdia mescaleroella sp. nov. has a conservative number and position of dorsal spines, the only difference observed is in the expression of the central spine.

Diagnosis
A species of Ceratobairdia with a lamellar overlap of LV over RV and a curved latero-ventral ridge delimiting a flat venter lacking a posterior spine.

Etymology
From the Latin 'sexaginta duo', meaning '62', referring to the location of the studied sections along the Highway 62.

Description
Massive carapace (H/L = 0.58-0.71); AB with small radius of curvature and maximum located at mid-H, dorsal part of AB forms a right angle with ADB at RV; VB straight at RV and convex at LV; PB short, with small radius of curvature located in lower ⅓ rd of Hmax; latero-ventral ridge developed along the VB; strong overlap of LV on RV particularly at DB developed into blade; surface smooth.

Remarks
Ceratobairdia sexagintaduella sp. nov. is similar to Bairdia monstrabilis Cooper, 1946 from the Pennsylvanian of Illinois (Cooper 1946) but differs by a shorter carapace, a shorter latero-ventral ridge and the presence of a blade along the dorsal overlap at LV. Noteworthy, Sohn (1954) considered that Bairdia monstrabilis Cooper, 1946 does not belong to Ceratobairdia mainly because of the lack of a dorsal structure at LV. Lobobairdia ventriconcava  in Chen & Bao, 1986 from the Early Permian of South China (Chen & Bao 1986) is similar to Ceratobairdia sexagintaduella sp. nov., but has an even shorter latero-ventral ridge and lacks the dorsal blade at LV. The morphology of the latero-ventral ridge in Ceratobairdia sexagintaduella sp. nov. is similar to that of Ceratobairdia sinensis Wang, 1978 from the Changhsingian, Late Permian of South China (Wang 1978) by the morphology of the lateroventral ridge but differs by lamellar DB at LV, PB less upturned and AB located lower. Ceratobairdia sexagintaduella sp. nov. is very similar to Bairdia permiana  from the Kungurian of the Glass Mountains : this species has later been shown to be a junior synonym of Bairdia pecosensis by Sohn (1960, who additionally mentioned that the ridge on the ventral part of the RV is not as pronounced as shown in the original drawing of .  Figs 9K-R, 10

Remarks
Most of the specimens of Ceratobairdia wordensis  in the present work occur as isolated valves and LV are relatively easily assigned to this species based on their unique dorsal ornamentation. The identification of RV is more complex and has been possible because of the description provided by Hamilton (1942: 716) of "the centrodorsal portion of the right valve flattens abruptly to hingeline, expressed as a flat terrace in dorsal bi and as a rather prominent ridge in lateral view; […]; the ventral portion of the right valve sharply infolded, forming a sharp downward projecting ridge terminating in mature molds as a backward projecting spine." Hamilton (1942: 716) described the dorsal margin of LV of Ceratobairdia wordensis as "usually ornamented by two to seven short strong spines equally spaced and concentrated dorsally on the middle third or more." The present material provided LV with 4 to 6 spines, but all other characters leave no doubt on the conspecificity of the specimens. Is the number of spines related to ontogeny? Although Hamilton (1942) mentioned 2 to 7 dorsal spines on LV, the unique specimen illustrated displays 6 spines and no discussion is provided on the possible link between size and number of the spines. Conversely, Sohn (1960: pl. 4 figs 12, 14, 17) illustrated specimens with 8 to 10 dorsal spines and at least one of them shows spines organized into 2 overlapping rows. For the present material, the number of spines along the dorsal margin of LV of Ceratobairdia wordensis ranges from 4 to 6 without pattern related to ontogeny (Fig. 10): • most of the smallest specimens, assigned to A-2?, are weathered but the two sufficiently well preserved at dorsal margin show 5 spines, the 2 external being 'embryonic', • the only known specimen of A-1? stage displays 4 dorsal spines, • the adult specimens display from 4 to 6 spines, the external ones being the smallest.
It is worth noting that in A-2? specimens, the external spines are very small and may be overlooked, leading to the wrong identification of only 3 dorsal spines. However, these specimens cannot be confused with Petasobairdia tricornuta Chen in Shi & Chen, 2002 from the Late Permian of South China (Shi & Chen 2002) which is more elongate, larger, and with only 3 spines for specimens of a size slightly larger than the adults of Ceratobairdia wordensis.
A significant morphological trend is observed in Ceratobairdia wordensis from the Guadalupe Mountains: whereas the majority of specimens have a relatively smooth surface, several show the development of scattered nodules in the dorsal area of their lateral surface (Fig. 9O-Q). This trend culminates in very rare specimens with the entire lateral surface of the valves covered by nodules (Fig. 9R). This nodular surface is reminiscent of Pustulobairdia Sohn, 1960 but all characters of Ceratobairdia wordensis and the morphological trend observed from smooth to nodular leave no doubt that these specimens belong to Ceratobairdia wordensis.  (Fig. 5G, only complete left valves measured, not considering spines).

Description
Sub-rectangular in lateral outline with Hmax around mid-L and Lmax around mid-H; dorsal margin uniformly convex with ADB straight and short; strong overlap of LV on RV along entire dorsal margin, much narrower along venter; PB steep, short and concave; dorsal margin transformed into nodular blade with 6 small triangular nodules; AB large with maximum of curvature around upper ⅓ rd and AVB plump, very convex; ventral margin straightly to slightly concave around mid-L; PB reduced, relatively large with maximum of curvature around mid-H; AB and PB slightly compressed laterally, prolonged by thick, short horizontal spines; surface smooth.

Remarks
Ceratobairdia pratti sp. nov. is unique among species of Ceratobairdia known to date by the disposition of nodules along a nodular blade at LV and by the spines terminating AB and PB.

Remarks
The carapace of this species is subtriangular in lateral view, with large AB and strong overlap of LV on RV, hemi-circular furrows are visible on the medio-anterior and medio-posterior parts of the carapace in both valves.
Genus Denticupachydomella Yuan in Yuan et al., 2009 Type species Denticupachydomella spinosa Yuan in Yuan et al., 2009 by original designation.

Original diagnosis
"A new Pachydomellidae genus with left valve having straight dorsal border, two horny dorsal spines erecting at the anterior cardinal angle, one stronger spine at the posterior cardinal angle, three denticles along dorsal border, one posteroventral spine and pustulous lateral surface." (from Yuan et al. 2009: 392-393).

Emended diagnosis
A new genus with a relatively massive postero-ventral spine, spines of various morphology and strength developed along the dorsal margin of the left valve and surface pustulose.

Assigned species
The following species are herein re-assigned to the genus Denticupachydomella:

Remarks
The thorough comparison of ornate Microcheilinellidae revealed that all the above-mentioned species share postero-ventral spines on both valves and spines/nodules/pustules along the dorsal margin and over the lateral surface. Conversely, the two horny dorsal spines and the three denticles along the dorsal border originally described by Yuan et al. (2009)

Description
Small carapace sub-rectangular, H/L = 0.57-0.69; DB straight on both valves; row of nodules long DB of LV; AB with quite large radius of curvature with maximum located below mid-H; VB almost straight at both valves; PB with large radius of curvature for genus with maximum of curvature located in lower part of H; presence of spine in posteroventral part of carapace; overlap of LV on RV all around carapace; presence of nodules on surface of both valves.

Remarks
Denticupachydomella bellcanyonensis sp. nov. is very similar to the type species Denticupachydomella spinosa Yuan in Yuan et al., 2009 from the Changhsingian of South China (Yuan et al. 2009) but is larger and lacks the two horny spines at the anterior and posterior cardinal angles. Denticupachydomella bellcanyonensis sp. nov. differs from Denticupachydomella multinodosa (Forel in Crasquin et al. 2010) from the Changhsingian (Late Permian) of Sichuan, south-west China (Crasquin et al. 2010) by the presence of a postero-ventral spine and by the organisation of nodules along dorsal and ventral margins at both valves. Herein, the dorso-central shoulder at RV is absent and the surface is covered by nodules. The species from the Late Capitanian of the Penglaitan section (Guadalupuan-Lopingian GSSP) in Guangxi, South China (Zazzali 2016: fig. 13o-p, unpublished material) differs from Denticupachydomella bellcanyonensis sp. nov. by a more elongate carapace and a PB with smaller radius of curvature. The species from the Penglaitan section is also new and has to be described.

Diversity and taxonomic composition of ostracod assemblages
Each of the 6 samples studied from the Middle Permian (Roadian and Capitanian) of the Guadalupe Mountains, West Texas, USA, yielded identifiable ostracods. In total, 51 species have been identified, belonging to 26 genera and 15 families. Seventeen species were previously known from the Permian, 11 are new and 23 are kept in open nomenclature due to poor preservation and/or paucity of material (including Microcheilinella sp. 15 in Zazzali et al. 2015, which occurs in the Wuchiapingian, Late Permian of South China). Table 1 provides a complete taxonomic list of the two assemblages from the Middle Permian (Roadian and Capitanian) of the Guadalupe Mountains. The assemblages described in the present contribution are obtained from two continuous bedded sections.
The autochthonous or allochthonous nature of ostracod assemblages can be assessed by considering the proportion of complete carapaces versus isolated valves and the demographic structure of populations (e.g., Oertli 1971;Boomer et al. 2003). As visible in all H/L scatter plots shown in Fig. 5 and Fig. 10, both assemblages are composed of a mixture of adults and juveniles, but very small juveniles are significantly lacking. Specimens were picked prior to this analysis and it is possible that only the largest specimens have been collected from the residues. In both assemblages, disarticulated valves are much more abundant than complete carapaces ( Fig. 5 and Fig. 10), indicating that relatively important transportation occurred, in line with the lithological information pointing to deep-water downslope deposits in the Roadian Quarry section (Amerman 2009;Hurd & Kerans 2014;Scholle et al. 2015). It is worth noting that none of the typical Palaeozoic off-shelf taxa (Beecherellidae Ulrich, 1894, Bythocytheridae Sars, 1866, Rectonariidae Gründel, 1962, Tricorninidae Blumenstengel, 1965 is present, which further confirms that these taxa may have been purely Palaeo-Tethyan in the Permian and the Triassic (Forel in press).

Stratigraphical and palaeobiogeographical distributions
Species restricted to the USA Several of the species reported from the present analysis were already known from other North American localities. Several species previously known only from the Early Permian are herein extended to the Middle Permian: • Kindlella fissiloba Sohn, 1954 previously only known from the Kungurian, Early Permian of Texas is herein shown to extend to the Roadian, • Bairdia rhomboidalis  documented from the Kungurian, Early Permian of Texas extends to the Capitanian, • Aurikirkbya wordensis , Bairdia subfusiformis  and Ceratobairdia wordensis  were only known from the Kungurian, Early Permian of Texas and are herein shown to occur in the Roadian and Capitanian, • Bairdia radlerae Kellett, 1934 known from the Asselian and Sakmarian, Early Permian of Kansas herein is documented from the Roadian and Capitanian.
Taxa with worldwide distributions Of the species recognized in the Middle Permian of the Guadalupe Mountains, several have been previously documented outside of this area during the Permian (Fig. 13). The present work extends the stratigraphical range of Microcheilinella postspinosa that was only known from the Kungurian, to the Capitanian. Conversely, Acratia sinuata, Roundyella lebaensis, Kindlella bellsundi and Microcheilinella sp. 15 in Zazzali et al. 2015 were only known from the Changhsingian, Late Permian, worldwide and herein are shown to have radiated in the Middle Permian. It is important to mention that stratigraphical updates are also observed at the generic level: until now Denticupachydomella was only known from the Late Permian but we show that it radiated in the Capitanian.
In terms of palaeobiogeographical distribution of taxa through time, several patterns are also visible. The species Sulcella mesopermiana, Petasobairdia campbelli, Fabalicypris glennensis and Microcheilinella postspinosa had a purely Palaeo-Tethyan distribution until the present contribution but their occurrence in the Middle Permian of the Guadalupe Mountains documents a transpanthalassic dispersal of species in the Permian. In the present state of our knowledge, these species all appear to have radiated on the eastern margin of Palaeo-Tethys sensu lato in the Early Permian (Fig. 13), but their dispersal patterns show significant discrepancies. Sulcella mesopermiana was restricted to the Indochina Block, Thailand ) and later spread westward to the eastern Palaeo-Tethys (Greece, Hungary) and eastward across the Panthalassa to the Guadalupe Mountains area in the Middle Permian. Conversely, Petasobairdia campbelli, Fabalicypris glennensis and Microcheilinella postspinosa only record a transpanthalassic eastward migration trend, but this feature may change with more data from diverse localities worldwide. A second group of species documents the opposite trend: Acratia sinuata, Roundyella lebaensis, Kindlella bellsundi and Microcheilinella sp. 15 in Zazzali et al. 2015 radiated in the Middle Permian of the Guadalupe Mountains area as revealed by the present assemblages and migrated westward to the Palaeo-Tethyan area in the Late Permian. These two migration ways herein illustrated for the first time show that exchanges of taxa between Palaeo-Tethys sensu lato and Panthalassa were strong in the Permian prior to the end-Permian extinction. The strong relationship of the northern America ostracod assemblages with the eastern Tethyan area, more precisely the South China Block, was already reported in Forel (2018). A second observation is that the eastern Palaeo-Tethys has been a zone of major importance in radiation of ostracod taxa in the Permian, as it was in the Triassic (Bate 1977;Kristan-Tollmann 1983Lord 1988;Ketmuangmoon et al. 2018;Forel et al. 2019;Forel & Moix 2020).

Conclusion
Ostracods of Roadian and Capitanian (Middle Permian) age have been extracted from samples collected from the Quarry and MKCS1 sections in the Guadalupe Mountains area in West Texas, USA. In total, the ostracod assemblages are composed of 49 species, which represent 26 genera and 15 families. Eleven new species are described: Healdia mckittrickensis Crasquin sp. nov., Healdia cutoffella Crasquin sp. nov., Aurikirkbya guadalupensis Crasquin sp. nov., Hollinella (Hollinella) williamsranchensis Crasquin sp. nov., Geisina culbersonensis Crasquin sp. nov., Paraparchites pecosensis Crasquin sp. nov., Bairdia elcapitanensis Forel sp. nov., Ceratobairdia mescaleroella Forel sp. nov., Ceratobairdia sexagintaduella Forel sp. nov., Ceratobairdia pratti Forel sp. nov., and Denticupachydomella bellcanyonensis Forel sp. nov. The Roadian and Capitanian assemblages are largely dominated by isolated valves that document transportation, in line with other proxies indicating deep-water downslope deposition. The stratigraphical and palaeobiogeographic distribution of taxa indicate transpanthalassic exchanges of taxa in the Permian as well as the importance of the eastern Palaeo-Tethys margin for radiation of ostracod species.