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).