Truncilla truncata Rafinesque, 1820
Truncilla truncata, INHS 4568. Sangamon River, Piatt County, Illinois.
Other common names Deerhorn.
Key characters Triangular shell, sharply angled posterior ridge, inflated, yellow, green, or brown, usually with numerous green rays.
Similar species Fawnsfoot, butterfly, Wabash pigtoe, elktoe.
Description Shell triangular, thin to moderately thick, and somewhat inflated. Anterior end rounded, posterior end bluntly pointed or truncated. Posterior ridge sharply angled. Umbos full and elevated well above the hinge line. Beak sculpture of three to five fine, double-looped ridges. Periostracum highly variable in color from yellow, green, yellowish brown to dark brown, with numerous green rays of variable widths and shape, often composed of fine broken lines or V-shaped or zigzag markings; occasionally rayless. Length to 2 inches (5.1 cm).
Pseudocardinal teeth well developed, elevated and divergent; two in the left valve, one in the right. Lateral teeth straight to slightly curved, high, roughened, occasionally with an incomplete, smaller inner lateral developed. Interdentum narrow or absent. Beak cavity shallow to moderately deep. Nacre white, occasionally pink, iridescent posteriorly.
Habitat Medium to large rivers in mud, sand, or gravel.
Status Widespread and common throughout much of its range. Species of Special Interest in Ohio.