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Ceratobairdia sexagintaduella Forel sp. nov. urn:lsid:zoobank.org:act: E353B465-EF88-46B2-A3E0-5C7C3B2AB411 Figs 5F, 9D–J 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 ‘s exaginta duo ’, meaning ‘62’, referring to the location of the studied sections along the Highway 62. Material examined Holotype USA • complete carapace, (Fig. 9D); Guadalupe Mountains, West Texas, Williams Ranch Member, Cutoff Formation, Quarry section, sample GM1; Roadian, Middle Permian; MNHN.F.F63440. Paratype USA • 1 left valve, (Fig. 9E); Guadalupe Mountains, West Texas, Williams Ranch Member, Cutoff Formation, Quarry section, sample GM1; Roadian, Middle Permian; MNHN.F.F63441. Additional material USA • 1 left valve; Guadalupe Mountains, West Texas, Williams Ranch Member, Cutoff Formation, Quarry section, sample GM1; Roadian, Middle Permian; MNHN.F.F63442 • 1 complete carapace; same locality as for preceding; Roadian, Middle Permian; MNHN.F.F63443 • 1 left valve; same locality as for preceding; Roadian, Middle Permian; MNHN.F.F63444 • 1 complete carapace; same locality as for preceding; Roadian, Middle Permian; MNHN.F.F63445 • 1 left valve; same locality as for preceding; Roadian, Middle Permian; MNHN.F.F63446 • 29 complete carapaces, 368 valves; Guadalupe Mountains, West Texas, Williams Ranch Member, Cutoff Formation, Quarry section, samples GM1, GM2; Roadian, Middle Permian; MNHN.F.F63496. Dimensions L= 753–1488 µm; H =389–925 µm (Fig. 5F, not all valves measured, all RV correspond to complete carapaces). 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. Occurrence Samples GM1, GM2, Quarry section, Williams Ranch Member, Cutoff Formation, Guadalupe Mountains, West Texas, USA, Roadian, Middle Permian (this work). 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 (Chen, 1958) 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 Hamilton, 1942 from the Kungurian of the Glass Mountains (Hamilton 1942): this species has later been shown to be a junior synonym of Bairdia pecosensis Delo, 1930 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 Hamilton (1942). |
