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THYASIRIDAE |
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Prothyasira benthicola Iredale, 1930 Description: Shape shell with a very strong posterior fold, a weak fold centrally and another anteriorly; height greater than width, umbo central, lunule large and shallow. Exterior with irregular commarginal growth ridges; no radial sculpture. Interior smooth, muscle scars not apparent, margin smooth. Hinge left valve without teeth, right valve with a single cardinal tooth, no marginal teeth. Ligament mainly internal, long, narrow. Shell colour white. Size: Largest syntype 12 mm in height. Distribution: Known only from the syntype lot consisting of three left valves plus one right valve from 33 miles (53 km) east of Green Cape, NSW, in 860 m. Habitat: Subtidal, 860 m depth. Comparison: This species is similar to Prothyasira peroniana but differs by having two weak folds extending from the umbo to the ventral margin, which makes the shell outline polygonal rather than smoothly rounded. The syntypes are from 860 m depth, substantially deeper than the deepest specimens of P. peroniana at 384 m. Remarks: In the original description of this species Iredale (1930) said that no cardinal tooth was present in the hinge. But examination of the right valve syntype (Shown only in exterior view in Fig. 1) shows a single cardinal is clearly present. Fig. 1: SYNTYPES 33 miles (53 km) east of Green Cape, NSW, in 860 m (C.047714) |
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