Pleurobema sintoxia (Rafinesque, 1820)
Other common names: Solid pigtoe, pink pigtoe, flat pigtoe, bullnose.
Key characters: A highly variable shell that is relatively large, rounded or elongate, chestnut or brown, with a shallow beak cavity.
Description: Shell moderately thick, round, and compressed (medium-sized rivers) to inflated (large rivers). Anterior end rounded, posterior end rounded to bluntly pointed. Dorsal margin straight to slightly curved, ventral margin usually curved. Umbos low and only slightly elevated above the hinge line. Beak sculpture of two or three elevated ridges on the umbo. Shell smooth. Periostracum greenish brown, light brown, or reddish brown in juveniles, becoming chestnut or dark brown in adults, with faint green rays visible near the beaks in some shells. Length to 4 inches (10.2 cm).
Pseudocardinal teeth well developed; two in the left valve, one in the right. Lateral teeth straight. Beak cavity shallow (medium-sized rivers) to moderately deep (large rivers). Nacre variable from white to pink or rose-colored.
Habitat: Medium to large rivers in mud, sand, or gravel.
Status: Widespread but usually uncommon. May be locally abundant in some drainages. Endangered in Iowa. Species of Special Interest in Ohio.