Ellipsaria lineolata (Rafinesque, 1820)
Other common names: None.
Key characters: Triangular, flattened shell, sharply angled posterior ridge, yellowish brown, with broken brown rays.
Similar species: Deertoe.
Description: Shell somewhat triangular, thick, solid, and compressed. Anterior end broadly rounded, posterior end pointed. Umbos compressed, directed forward, and not elevated above the hinge line. Posterior ridge sharply defined. Lateral surfaces broadly flattened, less so in older females. Beak sculpture, if visible, of a few fine, double-looped ridges. Shell smooth, yellow or yellowish green, with scattered brown rays that are usually broken into V-shaped or irregular rectangular blotches. Old shells with faint brown rays or rayless. Length to 4 inches (10.2 cm).
Pseudocardinal teeth relatively large, slightly elevated, serrated, and divergent; two in the left valve, one in the right. Usually two lateral teeth in each valve, serrated, short, and straight. Interdentum wide. Beak cavity shallow to moderately deep. Nacre white, iridescent posteriorly.
Habitat: Large rivers in sand or gravel.
Status: Widespread but only locally abundant. Disappearing from many areas where it formerly occurred. Endangered in Ohio and Wisconsin. Threatened in Iowa. Species of Special Concern in Illinois.