Shell moderately thick, round, and compressed (medium size 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 the 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 four inches.

Pseudocardinal teeth well developed; two in the left valve, one in the right. Lateral teeth straight. Beak cavity shallow (medium size rivers) to moderately deep (large rivers). Nacre variable from white to pink or rose colored.