Girtypecten ( Sinopecten ), 2006

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 : 601

Subgenus Girtypecten ( Sinopecten) nov.

Type species: Girtypecten ( Sinopecten) newelli sp. nov.; Tournaisian (Early Carboniferous), Guizhou, China .

Derivation of the name: Prefix Sino from Latin Sinae, oriental people mentioned by Ptolemy, and now generally applied to things pertaining to China and the Chinese; and the stem of Pecten , from the name of a Cenozoic scallop, and now widely applied to forming scallop names.

Species included: Acanthopecten chitralensis Reed, 1925 ( Reed 1925:

56, pl. 10: 4, Early Permian, India and Pakistan); Girtypecten spinosus Chen, 1962 ( Chen 1962: 194, pl. 1: 2a, b; Wuchiapingian, Late Permian, Guizhou, China); Girtypecten cf. spinosus (Lu, in Zhang et al. 1979: 228, pl. 58: 5; Maokouan, Middle Permian, Qinghai, China); Girtypecten cf. spinosu s ( Yin 1982: 354, pl. 30: 9; Changhsianian, Late Permian, Sichuan, China); Girtypecten carboniferus Zhang, 1987 ( Zhang 1987: 277, pl. 1: 7, 8, 10, 15, 16; early Mapingian, Late Carboniferous, Guangxi, China). Stratigraphic and geographic range: Tournaisian–Changhsingian; India, Pakistan, and China.

Diagnosis.—Unicostate Girtypecten with left valve often having pyramidal costal spines rising from the ridge intersections, distally pointed, with a dorsal groove along the outerside; resilifer asymmetrical, anteriorly elongate. Besides the unicostate ornamentation, the new subgenus differs from Girtypecten ( Girtypecten) in having resilifer positioned before the beak and costal spines with dorsal groove.

Description.—Shell suborbicular, nearly acline or slightly prosocline; auricles elongate, well differentiated from disc by umbonal fold; posterior auricle acute; only with simple, coarse, rounded primary costae, which are intersected by similarly spaced commarginal ridges to form reticulated ornamentation; the interspaces smooth, lacking costellae and/or lines; left valve often with costal spines rising from the ridge intersections, distally pointed, circular in cross section with a dorsal groove along the outerside; ligament area aviculopectinid−type, with a large resilifer, most of the resilifer lies before the beak.

Discussion.—As mentioned above, the resilifers in our specimens are mostly positioned before the beak ( Fig. 2A 2, A 3, B 2, C 2). Among them, the anterior part of the resilifer of B 2 is broken, the resilifer of C 2 is not well preserved, only A 3 is in best state of preservation. The resilifer of A 3 is relatively large, having a breadth of nearly 4 mm, with its larger part (3/4) before the beak. This is just the opposite of Girtypecten sublaqueatus ( Girty, 1908) , the type species of Girtypecten ( Girtypecten) Newell, 1938 . In the latter, the greater part of the resilifer lies behind the beaks ( Newell 1938: 77, pl. 13: 11; Newell and Boyd 1995, fig. 30: 2b, 4a, 6a). In addition, the costal spines on the left valve of G. ( G.) sublaqueatus have a ventral groove along the innerside ( Newell 1938: fig. 29). On the contrary, in our specimens the groove on costal spines is dorsally situated ( Fig. 2F).