A. purpurascens.
A. nucleola.
A. physioides.
A. glabrella. The smooth Amphidesma. Pl. [6], fig. 9.
Species lenticular or oval, with or without a lunated depression.
A. lactea. The milky Amphidesma.
Sub-orbicular, sub-pellucid, compressed, reticulated; yellowish white.
FAMILY VI.
Corbulacea. Two genera.
1. Corbula. Nine species.
This genus approximates the Crassatella and Ungulina, but is distinguished from them by the inequality of the valves and the strong primary tooth.