Scientia Sinica

106 SCIENTIA. SINICA Vol. V

west of Tangtishuya and Fenhsiang Villages, North-Ichang District, Hupel: Province.

Collectors: Y.S..Chi, T. Y. Hsu and the author.

Discussion: This pretty small species is quite abundant in the weathering slopes formed by the Neichia Series in the Gorge Region of Central China. The material consists mainly of complete individuals with well-preserved external characters. Separated valves are very scarce. It is associated with Yangtzeella poloi and Mimella formosa (sp. noy.).

This species resembles in several respects Martellia giraldi (Martelli)? from the Middle Ordovician, Shensi Province, but differs in having a less convexity of the valves and in possessing exceedingly faint, weak fold and sulcus, It is also recognized by its small size, never reaching more than 15 millimetres in width as exhibited by about 30 specimens in our collection.

Genus Hemipronites Pander 1830 ?Hemipronites hupeihensis Wang (sp. nov.)

(PI. II, D; Figs. 1-4) Shell rotund, outline subquadrate to subcircular; hinge-line shorter than the greatest width of the shell; cardinal extremities obtusely angular; beaks closely oppressed; lateral profile strongly and subequally biconvex; anterior commissure rectimarginate. Surface finely multicostellate, with about 3 costellae in 5 millimetres at the front of the shell; interspaces marked by

radiating rows of minute pits. ; Ventral valve strongly and evenly convex in lateral profile, with the greatest convexity at the middle; lateral and anterior margins rounded;

anterior profile flatly convex; umbo swollen; beak incurved; interarea short, apsacline, slightly curved.

Dorsal valve very strongly and evenly convex, the greatest convexity being at the middle; anterior profile gently convex; umbo flatly convex, slightly swollen; beak inconspicuous; interarea moderately long, orthocline.

The umbonal regions of both valves in this specimen have externally worn out, the dental plates and brachiophore supports exhibited as dark lines which are short and widely divergent.

Dimensions (mm): Length 27.5; width 31.2; thickness 21.1; hinge width 21.2.

Holotype, I.P.A.S. 8004.

Horizon and locality: Neichia Series, Middle Ordovician; Pankuchai, one mile west of Tangtishuya Village, Ichange District, Hupeh Province.

Collectors: T. Y. Hsu and the author.