Scientia Sinica

No. 1 WANG: NEW SPECIFS OF BRACHIOPODS [I] 169

width of the shell is near the anterior margin. Moreover, the lateral commissure of our form is commonly not flexed as in P. borealis, and the dorsal valve is nearly flat.

Pentamerus muchuanensis Wang (sp. nov.) (PI. IV, C; Figs. 1-4)

Shell moderately large, typically sub-globose; outline suboval, greatest width distinctly in front of the mid-length; subequally biconvex in lateral profile, with the ventral valve deeper; anterior margin broadly rounded, anterior commissure rectimarginate; hinge-line exceedingly narrow, usually equal to only one-fourth the greatest width of the shell. .

Ventral valve broadly convex, highest region a little posterior to the middle of the valve, curving sharply and steeply toward lateral margins, gradually and smoothly toward the anterior margin, and bending abruptly and vertically toward the umbo; umbo very prominent, globose; beak small, closely incurved against the dorsal valve.

Dorsal valve subtriangular in general outline; more strongly convex longitudinally than transversely, greatest convexity a little anterior to the umbo, sloping steeply posteroward but gently to the anterior margin; umbo somewhat tumid; beak strongly incurved, concealed under the delthyrium of the ventral valve.

Dimensions (mm): Length 45.4; width 412; thickness 325, hinge-width Hees

Holotype, I-P.A.S. 8011.

Horizon and locality: Lojoping Series, Middle Silurian; Muchuan. District, Kweichow Province.

Collector: 1. Huang.

Discussion: This species is represented by two specimens. The shell is considerably exfoliated with the umbonal region partially broken so that its internal structures are clearly exhibited. This species differs from Pentamerus dorsoplanus (sp. nov.) in having a relatively shorter shell length, in being subtriangular instead of subpentagonal in outline and in having a strong convex dorsal valve with no trace of sulcus.

Genus Clorinda Barrande 1879 Clorinda subaequata Wang (sp. nov.) (Pl. III, A; Figs. 1-5)

Shell medium size; transversely suboval in outline, greatest width about in mid-length; lateral and anterior margins rounded; subequally biconvex in lateral profile; anterior commissure strongly uniplicate.