Quadrula nodulata (Rafinesque, 1820)
Other common names: Two-horned pocketbook, winged pimpleback, pimpleback, nodule shell, winged orb shell.
Key characters: Rounded shell with two rows of paired knobs or pustules on the posterior half of the shell; no sulcus.
Description: Shell relatively thick, rounded, and inflated. Anterior end rounded, posterior end squared or truncated. Dorsal margin straight, area behind the umbos flattened into a small wing, ventral margin broadly rounded. Umbos rounded and elevated above the hinge line. Beak sculpture, if visible, of small ridges. Shell smooth except for two rows of knobs, usually occurring in pairs, that extend from the umbos to the ventral margin of the shell. No sulcus. Periostracum rayless and uniformly yellowish green or light brown, becoming darker with age. Length to 3 inches (7.6 cm).
Pseudocardinal teeth serrated and well developed; two in the left valve, one in the right (occasionally with a small tooth on either side). Lateral teeth short, heavy, serrated and straight to somewhat curved; two in the left valve, one in the right. Beak cavity deep. Nacre pearly white, iridescent posteriorly.
Habitat: Large rivers or in the lower sections of medium-sized rivers in sand or fine gravel.
Status: Uncommon, but locally abundant. Endangered in Ohio. Threatened in Wisconsin. Rare in Missouri.