Fusconaia subrotunda (Lea, 1831)
Other common names: Round-solid, pigtoe.
Key characters: Smooth, elongate, and solid shell; beak cavity very deep, green rays on the umbo.
Description: Shell relatively large, solid, elongate, oval or elliptical, and moderately inflated. Anterior end rounded, posterior end rounded or bluntly pointed. Dorsal margin and ventral margins straight to slightly curved. Umbos low and directed forward. Shell smooth, light brown, becoming dark brown to black in adults. Fine green rays present on juveniles and the umbos of older shells. Length to 5 inches (12.7 cm).
Pseudocardinal teeth large and well developed; two in the left valve, one in the right (occasionally with a small tooth on either side). Lateral teeth large and straight; two in the left valve, one in the right. Beak cavity very deep. Nacre white, iridescent posteriorly.
Habitat: Large rivers in gravel.
Status: Endangered in Indiana and Ohio. Extirpated from Illinois.