Monkeyface (Quadrula metanevra)

Shell Characteristics
Squarish, valves thick, inflated; prominent posterior ridge-often with a series of large knobs and surrounded by scattered pustules; posterior slope compressed, appearing winged- often with a series of small ridges that curve upward; posterior shell margin indented; periostracum yellowish, greenish or brown, usually marked with green chevrons. Teeth heavy, nacre white. Length to 5 inches. Similar to mapleleaf, pimpleback, purple pimpleback, wartyback, and winged mapleleaf.

Distribution and Habitat
Medium and large rivers in coarse substrate and flowing water. Extirpated from the Minnesota River and some southern steams, and rare in the Mississippi River below St. Anthony Falls. Best remaining populations are in the lower St. Croix River where it is locally common, but rarely abundant.  Commercially valuable.