Elliptio dilatata (Rafinesque, 1820)
1-3. St Joseph River, Williams Co., OH - 1: 93 mm; 2: 93 mm; 3: 88 mm
4. Wisconsin River, Crawford Co., WI - 92 mm
5. Black River, Lawrence Co., AR - 78 mm
6. Duck River, Marshall Co., TN - 88 mm
7. Sydenham River, Lambton Co., Ontario - 85 mm
8. New River, Wythe Co., VA - 83 mm
Type locality: Kentucky River.
Range: Mississippi River system; Great Lakes and portions of St Lawrence River system.
Remarks: Elliptio dilatata is the most widespread species in the genus. It is replaced by its obvious close relative arca in the Mobile system. The two species are very similar -- specimens of "dilatata" from west of the Mississippi River, particularly in Arkansas, resemble arca more than eastern dilatata.
Whereas most specimens have purple nacre, some populations across the species' range have purple, white, and salmon nacred individuals living side by side.