Bairdia elcapitanensis Forel sp. nov.

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Figs 7P–R, 8A–B

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.

Material examined

Holotype USA • right valve, (Fig. 8B); Guadalupe Mountains, West Texas, Williams Ranch Member, Cutoff Formation, Quarry section, sample GM1; Roadian, Middle Permian; MNHN.F. F63420.

Paratype USA • 1 right valve, (Fig. 7R); Guadalupe Mountains, West Texas, Williams Ranch Member, Cutoff Formation, Quarry section, sample GM1; Roadian, Middle Permian; MNHN.F. F63418.

Additional material

USA • 1 complete carapace; Guadalupe Mountains, West Texas, Williams Ranch Member, Cutoff Formation, Quarry section, sample GM1; Roadian, Middle Permian; MNHN.F. F63416 • 1 carapace; same locality as for preceding; Roadian, Middle Permian; MNHN.F. F63417 • 1 right valve; same locality as for preceding; Roadian, Middle Permian; MNHN.F.F634119 • 16 right valves; same locality as for preceding but samples GM1, GM2; Roadian, Middle Permian; MNHN.F. F63491.

Dimensions

L= 1250–1386 µm; H =635–761 µm.

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.

Occurrence

Samples GM1 and GM2, Quarry section, Williams Ranch Member, Cutoff Formation, Guadalupe Mountains, West Texas, USA, Roadian, Middle Permian (this work).

Remarks

Bairdia girtyi Sohn, 1960 sensu 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.