Shell oval, massive, very inequilateral, rounded before, highly arched above and rounded at base, very bluntly pointed behind. Sides flattish, constricted slightly or not at all, and the umbonal ridge usually obsolete. Epidermis brownish or somewhat horncolored, rayless, and the surface roughened with close growth-lines. Ligament darkened, heavy, short and much elevated. Beaks pointed, small and very low. Beak cavity shallow, extending slightly under both cardinal and lateral teeth, thus making it very broad and with obtusely rounded sides. Cardinal teeth double in the left valve, single in the right and smoothish, or crested and short. Lateral teeth heavy, slightly curved, wide apart, arising from a thick dorsal plate. The cardinal of right valve with an oblong groove at its base. Cicatrices distinct ; dorsal cicatrices confluent into an oblong groove under the dorsum. Pallial impression deep and denticulate. Nacre usually pure white, often more or less with waxy discoloratious or mottlings or even dirty white.
[Wright, 1897. Original description]