Page:Walcott Cambrian Geology and Paleontology II.djvu/130

74 varying width. A dorsal valve shows a few fine, faint, radiating ridges.

A ventral valve 3 mm. in width has a length of 2.75 mm. and a height of 1 mm. A dorsal valve with a width of 2.5 mm. has a length of 2 mm. and a height of 0.5 mm. at the beak.

Observations.—In form the ventral valve of this species is not unlike that of Micromitra sculptilis (Meek) except that it is not as elevated and its surface is quite different. It is associated with M. sculptilis and the two varieties of Micromitra (Iphidella) pannula,—ophirensis and maladensis.

Formation and locality.—Middle Cambrian: Fu-chóu series; (35n and 35r) limestones and (36d) shales near the base just above the white quartzite, collected in a low bluff on the shore of Tschang-hsing-tau island, east of Niang-niang-kung, Liau-tung, Manchuria, China.

Collected by J. P. Iddings and Li San.

This species and Lingulella marcia belong to a group of small, elongate, oval shells that are represented in the Rocky Mountain Province Cambrian fauna by Lingulella manticula (White) and in the Atlantic Province fauna by L. atava (Matthew), L. collicia (Matthew), L. ferruginea (Salter), L. nanno (Walcott), and a number of similar forms. Lingulella manchuriensis appears to be most nearly related to L. similis (Walcott). It differs in the broader, more rounded posterior half of the ventral valve.

The average length of the ventral valve is 3 mm. among the large number of shells that occur in both limestone and shale.

Formation and locality.—Middle Cambrian: (35p) Fu-chóu series; shales about 80 feet (24 m.) above the white quartzite, collected in a low bluff on the shore of Tschang-hsing-tau island, east of Niang-niang-kung, Liau-tung, Manchuria, China.

Collected by J. P. Iddings and Li San.

This species is one of the small forms allied to the group of similar shells mentioned under L. manchuriensis. It differs from the latter species in being relatively broader in outline, with the sides of the valves less uniformly arched, and in having a more broadly rounded frontal margin.