Potamilus purpuratus shell description:

“ Shell very large, somewhat obovate, inflated, with full, high beaks, having very faint, corrugated sculpture, scarcely winged in front, with a low, angular wing behind; there are two or sometimes three low, radiating ridges on the posterior slope; surface nearly smooth or somewhat sulcate, covered with a shining, blackish epidermis; ligament large and long, generally exposed in adult shells; left valve with two subcompressed to solid, ragged pseudocardinals and two strong, remote laterals, the hinge line rounded between the two sets of teeth; right valve with two pseudocardinals, the lower the larger, and one strong, truncated lateral; beak cavities rather deep, with a row of deep scars running towards the anterior base; muscle scars large, the anterior deep and smooth, the posterior scarcely impressed; nacre rich, dark purple, somewhat iridescent behind, much thicker in front.  Male shell full at the posterior base, rounded and obtusely biangulate behind above the median line; the female shell has a wide, rounded, marsupial swelling far behind, and is decidedly truncate posteriorly ”(Simpson, 2014; Mather, 2007).