Scientia Sinica

170 SCIENTIA SINICA Vol. V

Ventral valve moderately convex, curving gradually toward the anterior margin and steeply toward the lateral and the cardinal margins; sulcus narrow and well defined, originating from the beak and widening rapidly anteroward, equal to about one-third the width of the valve in the front margin; beak small, incurved.

Dorsal valve flatly convex, greatest convexity near the umbo; median fold prominent and sharply defined, originating from the beak and increasing in width anteriorly until it occupies about one-third the width of the valve, top rounded and highly elevated at the front; beak minute, incurved.

Dimensions (mm): Length 13.0; width 14.6; thickness 13.0. Holotype, I-P.A.S. 8012.

Horizon and locality: Upper Silurian; Hueichenkou, near Changning City, southwestern Szechwan Province.

Collector: LL. T. Yeh.

Discussion: This species can be recognized readily by its transversely oval outline and less convexity in both valves. Generally, this species resembles Clorinda linguifera (Sowerby) in having a transversely oval outline, but differs from that species in its smaller size, more sharply defined fold and sulcus, and less convexity in lateral profile.

Genus Camarotoechia Hall and Clarke 1893 Carmarotoechia fengkangensis Wang (sp. nov.) (Pl. V, B; Figs. 15)

Anastrophia fengkangensis, Wang: Index Fossils of China (Invertebrate), pt. Il, p. 129, pl. 68, figs. 25, 26. .

Shell medium size; subquadrate to subpentagonal in outline, lateral margins broadly rounded; subequally biconvex in lateral profile; anterior commissure strongly uniplicate. Surface covered by simple plications, fine on the beak and strongly subangular toward the anterior margin, five on fold and four in sulcus, with 12-13 on each lateral slope, two additional plications extend beside the fold and sulcus and die out a little anterior to the middle of the valve.

Ventral valve gently convex, highest region posterior to the middle of the valve, elongately elevated in umbonal region, sloping steeply to the anterior and lateral margins; median portion depressed anteriorly to form a very broad and deep sulcus, about equal to one-third the width of the valve, continued anteriorly into a short tongue-shaped prolongation; umbo narrowly convex; beak prominent, pointed, erected and incurved.

Dorsal valve broadlv and evenly convex, highest at mid-point whence surface descends gradually to lateral margins; umbo broadly convex; beak