Valve ovate; costæ short, marginal, radiate, 3-6 in 10 µ, often unequal; central area ovate, indistinctly costate; striæ scarcely visible, about 18 in 10 µ; pseudoraphe narrow. L. 45-93 µ.
Surirella davidsonii A. S.
Fresh or brackish water.
Pl. [35], Fig. 5; Pl. [39], Fig. 11.
The smaller specimen is from the Delaware River, and the larger from the Hudson River.
SURIRELLA CRUMENA BRÉB.
Valve nearly orbicular; costæ short, marginal, radiate; pseudoraphe narrow, indistinct; central area indistinctly costate, sometimes interrupted.
On account of the extreme confusion in the names of many forms which appear to be variations of S. ovalis, I have followed Van Heurck in retaining the original names as specific. De Toni gives S. crumena as a variety of S. ovalis.
Fresh and brackish water. Quite common in the Delaware River.
Pl. [35], Fig. 4.