The shell is inequivalved and displays variable forms, typically semioval or subcircular, transverse or elongate, and can be plano-convex or concavo-convex. The hinge-line may sometimes equal the greatest width of the shell. The ventral valve is convex or subangular in the middle, with a moderately incurved and more or less extended beak; the foramen is terminal, formed on the lower side by two deltidial pieces. The dorsal valve can be flat, convex, or depresso-convex. A mesial fold and sinus are usually present but not often prominently expressed. The shell structure is lamellose or fibrous, lacking punctuations. Valves articulate through two robust teeth in the ventral valve, inserted into sockets in the dorsal valve, mainly excavated in the base of a strong cardinal process. The teeth converge and are denticulate, matching corresponding denticulations in the sockets. Muscular impressions reveal a large oral or flabelliform area with a thin median septum, and small adductor imprints are present.