Strophomenoidea King, 1846

Zhan, Renbin & Jin, Jisuo, 2005, Brachiopods from the Middle Ordovician Shihtzupu Formation of Yunnan Province, China, Acta Palaeontologica Polonica 50 (2), pp. 365-393 : 385-386

Superfamily Strophomenoidea King, 1846 Family Strophomenidae King, 1846

Strophomenid gen. et sp. indet.

Fig. 13J ; Table 14.

Material.—One dorsal internal mould.

Description.—Shell medium−sized, subsemicircular, gently concave with nearly planar visceral area. Interarea low, catacline. Notothyrium relatively wide, covered by thin, arched chilidium ( Fig. 13J 2 ). Cardinalia about one−tenth length and one−third width of shell; two lobes of cardinal process small, discrete, rod−like, sitting on highly elevated notothyrial platform, projecting ventrally and posteriorly; sockets shallow, open antero−laterally; socket ridges thick, low, divergent from each other at 129 degrees, curving postero−laterally. Muscle field weakly impressed, bounded postero−laterally by pair of thin side septa.

Discussion.—The only dorsal valve available has Type A cardinalia ( Rong and Cocks 1994; Cocks and Rong 2000) and weak transmuscle ridges, which confirm its affinity to Strophomenidae . Platymena ? mutabilis Xu, Rong, and Liu, 1974 from the Shihtzupu Formation of northern Guizhou Province is similar to the Weixin specimen in its nearly flat dorsal valve with similar cardinalia and postero−lateral muscle bounding ridges, but differs in having a semicircular outline and a low, thin, dorsal median septum.

Figures

Fig. 13. A–I. Leptestiina veturna sp. nov. A. NIGP139145, paratype, ventral internal mould. B. NIGP139146, paratype, ventral internal mould. C. NIGP139147, holotype, ventral internal mould (C1) and latex cast (C2). D. NIGP139148, paratype, ventral internal mould. E. NIGP139149, paratype, ventral internal mould (E1) and latex cast (E2). F. NIGP139150, paratype, dorsal internal mould. G. NIGP139151, paratype, three dorsal external moulds, with dorsal external mould of Leptellinidae gen. et sp. nov. (to be erected by Zhan and Jin in press) (second from right). H. NIGP139152, paratype, dorsal external mould (H1) and latex cast (H2); note also ventral interarea. I. NIGP139153, paratype, broken dorsal internal mould. J. Strophomenid gen. et sp. indeterminate; NIGP139154, dorsal internal mould (J1) and latex cast (J2), together with a dorsal internal mould of Leptellina spatiosa sp. nov. (top).

Fig. 2. Middle Ordovician sedimentary facies on the Yangtze Platform, South China palaeoplate (modified from Zhang et al. 2002), with three fossil localities discussed in the text: 1, Shihtzupu Formation at Shizigou Valley near the Weixin County town, Yunnan Province; 2, Type area of Shihtzupu Formation at Donggongsi, Zunyi, Guizhou Province; 3, Dashaba Formation at Shuanghe, Changning, Sichuan Province.