Lampsilis ovata (Say, 1817)
Lampsilis ovata, INHS 1076 (Ohio River, Alexander County, Illinois) and UIMNH Z-4021 (Duck River, Maury County, Tennessee).
Other common names Sharp-ridged pocketbook, southern pocketbook, grandmaw.
Key characters A round or oblong shell, inflated, posterior end bluntly pointed in males and truncated in females; prominent, sharply angled posterior ridge; outer surface smooth, yellow or tan, and usually rayless except on the posterior slope.
Description Similar in shape to the plain pocketbook. Shell relatively large, rounded or oval, thin to moderately thick, and inflated. Anterior end rounded, posterior end bluntly pointed in males, truncated in females. Dorsal margin straight, ventral margin curved. Umbos elevated above the hinge line. Prominent, sharply angled posterior ridge present. Shell smooth, yellow or yellowish brown, darker on the posterior slope, with rays largely absent in adults except for a few thin green lines on the umbos and posterior slope. Length to 6 inches (15.2 cm).
Pseudocardinal teeth thick, compressed and elevated; two in the left valve, one in the right. Lateral teeth curved and short. Beak cavity large and deep. Nacre white, iridescent posteriorly.
Habitat Large rivers in coarse sand or gravel.
Status Rare in the Ohio River and some of its larger tributaries. Endangered in Ohio. Likely extirpated from Illinois.