Valve elliptical; marginal costæ short, 3 in 10 µ; striæ delicate, 18 in 10 µ; undulations four or more. L. 70-140 µ.
Blue clay.
Pl. [37], Fig. 1.
Forma spiralis.—Valve ovate, swelled into curved ridges at the lower end, with a contraction of the valve.
Port Penn, Delaware River.
Pl. [37], Fig. 2.
CYMATOPLEURA MARINA LEWIS
Frustule linear, with numerous undulations, ends apiculate; valve linear-lanceolate, with acute ends; striæ transverse, punctate at unequal intervals, from 16-18 in 10 µ. L. 43 µ.
East River, N. Y.
Pl. [37], Figs. 3 and 4.