Illinois Natural History Survey - University of Illinois

Epioblasma rangiana (Lea, 1839)

Northern riffleshell

Epioblasma rangiana, INHS 1675. White River, Indiana.
Length: 1.8 inches (4.6 cm) for both male (top) and female (bottom).

Other common names White-mouth riffleshell.

Key characters Males and females yellowish brown or green but much different in shape. Males oblong with a sulcus running along the posterior ridge from the umbo to the ventral margin. Females with a large expanded posterior end. Tubercles on the lateral surface greatly reduced or absent.

Similar species Tubercled blossom.

Description Shell elongate, thick anteriorly, much thinner posteriorly, and compressed. Anterior margin rounded, posterior-ventral margin broadly rounded in females, indented in males. Umbos low, somewhat turned forward. Tubercles or knobs on the lateral surface greatly reduced or absent. A wide, shallow sulcus or depression present between the posterior and medial ridges. Periostracum yellowish brown with numerous fine green rays, obscure in older shells. Length to 2 inches (5.1 cm).

Pseudocardinal teeth triangular, divergent, and roughened; two in the left valve, one in the right, with two smaller teeth on either side. Lateral teeth moderately long, straight, and roughened; two in the left valve, one in the right with a much smaller tooth below. Beak cavity moderate to shallow. Nacre white, iridescent posteriorly.

Habitat Medium to large rivers in gravel riffles.

Status Proposed for Federal Endangered status. Endangered in Indiana, Michigan, and Ohio. Extirpated from Illinois.

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