Girtypecten Newell, 1938

Fang, Zong-Jie, Sun, Yuanlin & Baliński, Andrzej, 2006, A new aviculopectinid bivalve from the Early Carboniferous of Guizhou, China, Acta Palaeontologica Polonica 51 (3), pp. 599-604 : 600-601

Genus Girtypecten Newell, 1938 [emended]

Type species: Aviculopecten sublaqueatus Girty, 1908 ; original designation by Newell (1938: 77).

Emended diagnosis.—Shell subcircular, prosocline or acline, left valve more convex than right, auricles elongate, sometimes acuminate, well differentiated from disc; disc surface marked only with simple, coarse, widely spaced primary costae (unicostate) or having ranks of new costae added by intercalation during growth (multicostate). Costae and similarly spaced commarginal ridges cross each other and produce a reticulated ornamentation of squares and rectangles; left valve often with costal spines rising from the ridge intersections, distally pointed, circular in cross section with an innerside (ventral) or outerside (dorsal) groove; right valve spineless. Alivincular ligament with posteriorly or anteriorly elongate asymmetrical resilifer.

Discussion.— Newell and Boyd (1995) employed terms such as multicostate, unicostate, and uniplicate in describing radial ornamentation in pectinoid bivalves and utilized these characters for their diagnoses and classification. They brought multicostate into the definition of the genus Girtypecten Newell, 1938 as an important character, but they did not mention the existence of unicostate species, such as Girtypecten spinosus Chen, 1962 . Therefore, it is necessary to emend the diagnosis of Girtypecten to accommodate both multicostate and unicostate species. A new subgenus Girtypecten (Sinopecten) is here proposed for the unicostate species of Girtypecten , while Girtypecten (Girtypecten) is appropriate for multicostate species such as the one described by Newell and Boyd (1995: 41).

The genus Acanthopecten is also characterized by distally pointed spines, which, however, are located between ribs and are externally concave, unlike the pyramidal costal spines of Girtypecten .