Squarish, valves thick, moderately inflated; well developed posterior wing with radiating ridges; two rows of pustules or larger tubercles separated by a sulcus extend from beak to the ventral margin; periostracum brown, young with faint rays. Teeth well developed, nacre white. Length to 4 inches. Similar to mapleleaf, monkeyface, and purple wartyback.
Distribution and Habitat
Medium and large rivers in sand and gravel and strong current. Historically occupied Mississippi, Minnesota, and lower St. Croix rivers. Now extant only in a small reach of the lower St. Croix River where it is rare.