Cumberlandia monodonta (Say, 1829)
Other common names: None.
Key characters: Elongate shell, usually pinched in the middle, dark brown to black, with poorly developed teeth.
Description: Shell oblong, elongate, and compressed. Anterior and posterior ends rounded. Ventral margin usually arched or pinched, occasionally straight. Shell thin in young, becoming thicker in older individuals. Umbos only slightly elevated above the hinge line. Beak sculpture, when visible, of three or four heavy ridges. Surface of shell smooth to somewhat rough, brown in young shells, becoming dark brown to black and rayless with age. Length to 8 inches (20.3 cm).
Pseudocardinal teeth small, tubercular; one in each valve in young individuals. Lateral teeth poorly developed or absent. Beak cavity moderately shallow. Nacre white, iridescent in young individuals and on the posterior fourth of shell in adults.
Habitat: Large rivers with swiftly flowing water, among boulders in patches of sand, cobble, or gravel in areas where current is reduced.
Status: Widely distributed but absent from many areas where it formerly occurred. Federal Candidate (Category 2). Extirpated from Ohio and possibly Indiana. Endangered in Illinois, Iowa, and Wisconsin. Watch List in Missouri.