1-3. Sipsey River, Tuscaloosa Co., AL - 1: 73 mm; 2: 75 mm; 3: 49 mm
4. Tombigbee River, Lowndes Co., MS - 70 mm
5. Cahaba River, Bibb Co., AL - 66 mm
6. Conasauga River, Murray/Whitfield Co., GA - 57 mm
Elliptio arca (Conrad, 1834)
1-3. Sipsey River, Tuscaloosa Co., AL - 1: 73 mm; 2: 75 mm; 3: 49 mm
4. Tombigbee River, Lowndes Co., MS - 70 mm
5. Cahaba River, Bibb Co., AL - 66 mm
6. Conasauga River, Murray/Whitfield Co., GA - 57 mm
Type locality: Alabama River.
Range: Mobile River system.
Remarks: This species is very closely related to dilatata, and in fact there is little to separate them except for their ranges. The two species even share the peculiar polymorphism in nacre color evident in some populations where individuals having purple, white, or salmon nacre live side by side. No other Elliptios have this feature. Elliptio arca is usually heavier, with a tendancy to be more rayed than most dilatata, but there are many exceptions.