Utterbackia imbecillis shell description:

"Shell oblong, thin, with dorsal and ventral lines nearly parallel, pointed behind at or above the median line, inequilateral, convex or inflated; beaks compressed or flattened, not projecting above the nearly or quite straight dorsal line, their sculpture consisting of a few rather feeble, irregular, broken ridges, which are sometimes faintly doubly looped; posterior ridge low, curved down in the middle; epidermis generally smooth, yellowish-green or blue-green, often banded and feebly rayed, with two or more wide, ill-defined, dark rays, on the posterior slope; muscle scars scarcely visible; nacre pale blue or bluish-white” (Simpson, 1914; Mather, 2007).