Ceratobairdia wordensis (Hamilton, 1942) Figs 9K–R, 10 Bairdia wordensis Hamilton, 1942: 716, pl. 110 fig. 4. Ceratobairdia wordensis – Sohn 1954: 5; 1960: 69, pl. 4 figs 8–17. Material examined USA • 1 left valve; Guadalupe Mountains, West Texas, Williams Ranch Member, Cutoff Formation, Quarry section, sample GM1; Roadian, Middle Permian; MNHN.F. F63447 • 1 left valve; same locality as for preceding; Roadian, Middle Permian; MNHN.F. F63448 • 1 left valve; same locality as for preceding; Roadian, Middle Permian; MNHN.F. F63449 • 1 right valve; Guadalupe Mountains, West Texas, ‘ McKittrick Canyon’ Member, Bell Canyon Formation, MKCS1 section, sample 4 (GM5); Capitanian, Middle Permian; MNHN.F. F63450 • 1 right valve; Guadalupe Mountains, West Texas, Williams Ranch Member, Cutoff Formation, Quarry section, sample GM1; Roadian, Middle Permian; MNHN.F. F63497 • 1 right valve;same locality as for preceding; Roadian, Middle Permian; MNHN.F. F63451 • 1 left valve; same locality as for preceding; Roadian, Middle Permian; MNHN.F. F63452 • 1 complete carapace; Guadalupe Mountains, West Texas, ‘ McKittrick Canyon’ Member, Bell Canyon Formation, MKCS1 section, sample 4 (GM5); Capitanian, Middle Permian; MNHN.F. F63453 • 1 broken carapace, 20 left valves; Guadalupe Mountains, West Texas, Williams Ranch Member, Cutoff Formation, Quarry section, samples GM1, GM2, and GM3; Roadian; MNHN.F. F63660 • 3 broken carapaces, 15 left valves; same locality as for preceding; ‘ McKittrick Canyon’ Member, Bell Canyon Formation, MKCS1 section, samples 4 (GM5) and 2 (GM6), Capitanian; Middle Permian; MNHN.F. F63498. Dimensions L= 727–1450 µm; H= 397–920 µm (Fig. 10, not considering spines). Occurrence Glass Mountains, Texas, USA, Roadian, Middle Permian (Hamilton 1942; Sohn 1954, 1960); samples GM1, GM2, and GM3, Quarry section, Williams Ranch Member, Cutoff Formation, Roadian; samples 4 (GM5) and 2 (GM6), MKCS1 section, ‘McKittrick Canyon’ Member, Bell Canyon Formation, Capitanian; Guadalupe Mountains, West Texas, USA, Middle Permian (this work). Remarks Most of the specimens of Ceratobairdia wordensis (Hamilton, 1942) 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.

Published as part of Tarnac, Anaëlle, Forel, Marie-Béatrice, Nestell, Galina, Nestell, Merlynd & Crasquin, Sylvie, 2021, Middle Permian ostracods (Crustacea) from the Guadalupe Mountains, West Texas, USA, pp. 1-60 in European Journal of Taxonomy 770 on pages 38-40, DOI: 10.5852/ejt.2021.770.1499, http://zenodo.org/record/5536263