Lasmigona complanata (Barnes, 1823)
Other common names: Pancake, razorback, elephant-ear, hackle-back.
Key characters: Large, rounded, compressed, relatively thin shell, bluntly pointed at the posterior end; dark brown or black periostracum, double-looped beak sculpture, and white nacre.
Description: Shell large, rounded, and compressed, very thin in young individuals, becoming slightly thicker in adults. Anterior end rounded, posterior end rounded to bluntly pointed. Dorsal margin straight with a large wing, often with several folds or ridges that extend to the side of the shell. Ventral margin straight to slightly curved. Umbos small, flattened, not projecting above the hinge line. Beak sculpture of four to six distinct, double-looped bars. Shell smooth except on the wing. Periostracum green or greenish brown in young shells, often faintly rayed, dark brown to black in old shells. Length to 8 inches (20.3 cm).
Pseudocardinal teeth well developed; two in the left valve, one (occasionally two) in the right. Lateral teeth poorly developed in both valves, represented as ridges or thickenings of the hinge line. Beak cavity shallow to moderately deep. Nacre bluish white or white, iridescent posteriorly.
Habitat: Pools or sluggish streams with a mud, sand, or fine gravel bottom.
Status: Widespread and common.