760


Journal of Paleontology 92(5):751–767 Type species.—Schizambon typicalis Walcott, 1884.


Schizambon langei new species Figure 5.1–5.14


Holotype.—Dorsal valve NPL 45507 (Fig. 5.9–5.11), sample LR-1520, Threadgill Member of the Tanyard Formation (Lower Ordovician, Cordylous angulatus conodont Zone and the Loxodus bransoni Subzone of the Rossodus manitouensis condont Zone), Texas.


Diagnosis.—Ventribiconvex shell with faintly sulcate dorsal valve. Apsacline ventral psedudointerarea. Well-developed median buttress elongated into short median septum tapering into low median ridge on dorsal valve. Ornament of radiating parvicostellae intersecting with pronounced concentric lamel- lae, at whose intersection low nodes and pustules are developed, not extending into spines.


Occurrence.—In the Cordylous angulatus conodont Zone and the Loxodus bransoni Subzone of the Rossodus manitouensis


Figure 5. Schizambon langei n. sp., from LR-1520 in the Loxodus bransoni Subzone of the Rossodus manitouensis condont Zone, in the Threadgill Member of the Tanyard Formation, Texas; scale bar is 1mm unless indicated otherwise: (1) ventral valve exterior (NPL 85577); (2–4) ventral valve oblique view of exterior, ventral interarea and formamen from posterior, detail of foramen (NPL 85578); (5–8) ventral valve interior, oblique view of interior, interior view from anterior, detail of interarea from posterior (NPL 85579); (9–11) dorsal valve (holotype) exterior, oblique view of exterior, detail of detail of postlarval ornament (NPL 45507); (12–14) dorsal valve interior, oblique view of interior, detail of pseudointerarea, (NPL 45506). Schizambon sp., from the Iapetognathus and Cordylodus angulatus conodont zones and the Symphysurina trilobite Zone, in the upper part of the San Saba Member of the Wilberns Formation and the lowest part of the Threadgill Member of the Tanyard Formation, Texas; scale bar is 500 μm: (15, 16) dorsal valve from LR-152 interior, exterior (NPL 45509); (17, 18) ventral valve from LR-1468 view of exterior, oblique view of exterior (NPL 45508).


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