Cyprogenia stegaria Rafinesque, 1820
Other common names Eastern fanshell, Ohio fanshell, pimpleback, ringed wartyback.
Key characters Rounded shape, numerous pustules, elevated growth lines, broken green rays.
Similar species Pimpleback, purple pimpleback.
Description Shell rounded, solid, and moderately inflated. Anterior margin rounded, posterior margin bluntly rounded or truncated. Ventral margin broadly rounded. Umbos not elevated above the hinge line. Beak sculpture, if visible, of a few weak ridges. Growth lines appear as distinct elevated ridges. Numerous pustules usually concentrated in the center but occasionally covering the entire surface of the shell. Periostracum usually greenish yellow, with a pattern of dark green rays made up of numerous smaller broken lines or dots. Length to 3 inches (7.6 cm).
Pseudocardinal teeth relatively large and serrated; two in the left valve, one in the right. Lateral teeth roughened, straight to slightly curved, heavy and very short. Interdentum wide. Beak cavity shallow to moderately deep. Nacre white, iridescent posteriorly.
Habitat Medium to large rivers in gravel riffles.
Status Federally Endangered.