Scientia Sinica

172 SCIENTIA SINICA Vol. V

Horizon and locality: Upper Devonian; Itate, Pohsi, Huaning District, Yunnan Province. Collectors: Students of Chungshan University.

Discussion: Paurorhyncha squamosa appears to be closely related to P. sp. figured in plate 119 of the Index Fossils of North America, from which it differs in the subrectangular outline instead of subtriangular, the most convex umbonal region of the dorsal valve, the narrower and shorter median fold, and the wide lateral flanks of both valves.

Paurorhyncha depressa Wang (sp. nov.) (Pl. V, D; Figs. 1-5)

Shell large; typically rectangular in outline; cardinal and antero-lateral angles broadly rounded; lateral profile lenticular, subequally biconvex, the dorsal valve having a little greater convexity; anterior commissure uniplicate.

Ventral valve moderately convex around the umbonal region, but flattened in lateral fanks; sulcus broad, bottom flat, originating as a shallow depression about in middle of the valve, becoming deeper and bending abruptly at the front to form a short and sharp tongue, extremity of the tongue being truncated; beak small, incurved.

Dorsal valve gently convex in lateral profile and most convex along the medial region of the valve; fold low and broad, equal to about one-third the shell width; umbo tumid; beak incurved.

Dimensions (mm): Length 31.4; width 48.0; thickness 15.0; hinge-width 22.6.

Holotype, I-P.A.S. 8015.

Horizon and locality: Upper Devonian; Itate, Pohsi, Huaning District, Yunnan Province.

Collectors: Students of Chungshan University.

Discussion: This species is associated with Paurorhyncha squamosa (sp. nov.). It differs from the latter in the general outline and the lateral profile. In the first place, the general outline of this species is rectangular rather than oval, and the maximum length is about only two-thirds the width of the valve. It differs from P. squamosa, moreover, in having a much less convexity of both valves. :

Genus Hypothyridina Buckman 1906 Hypothyridina hunanensis Wang (sp. nov.) (Pl. V, C; Figs. 15)

Shell of medium size; subpentagonal in outline, shape subcuboidal ; width a little greater than length, with the greatest width about along the cardinal