Strophitus undulatus shell description:

“Shell generally subrhomboid, scarcely inflated, rather thin, inequilateral, with high beaks, whose sculpture consists of a few very strong ridges running parallel with the growth lines, turning up somewhat behind; behind these there are usually a few radial lirae; posterior ridge generally well developed and angular, sometimes double; surface with fine growth lines; epidermis dull ashy, ashy-green or smoky, often with faint, darker rays; hinge line narrow, somewhat incurved in front of the beak, having the merest vestiges of pseudocardinals and no laterals; beak cavities not deep; nacre bluish, often straw-colored, buff or pale salmon in the shell cavities  ”(Simpson, 2014; Mather, 2007).