Obovaria retusa (Lamarck, 1819)
Other common names: Golf stick.
Key characters: Thick shell, recurved umbos, brown periostracum, nacre purple inside the pallial line.
Similar species: Ebonyshell, round pigtoe, round hickorynut, hickorynut.
Description: Shell thick, solid, and somewhat inflated, with an unusual dorso-ventrally elongated recurved shape. Anterior, ventral, and posterior margins rounded. Umbos high, full, swollen, and directed forward. Shell surface smooth or clothlike. The female has a distinct groove on the posterior ridge. Periostracum reddish brown, occasionally dark brown or blackish. Length to 3 inches (7.6 cm).
Pseudocardinal teeth large, elevated, heavy, and serrated; two in the left valve, one large one in the right, often with a smaller tooth on either side. Lateral teeth short, straight to slightly curved, and serrated. Interdentum moderately wide. Beak cavity deep. Nacre pink or purple within the pallial line, white around the margins.
Habitat: Large rivers in gravel or sand.
Status: Federally Endangered. Extirpated from the Midwest.