Toxolasma texasiense shell description:

“Shell long elliptical or subcylindrical, generally a very little wider behind, inflated, subsolid, with full, but not high, beaks, which are turned forward over a narrow lunule, their sculpture consisting of seven or eight single-looped ridges, which are curved up more behind than in front, and return at the posterior end in converging lines to the nucleus; posterior ridge wanting; epidermis thick and cloth-like, blackish or fuscous, often brownish in the umbonal region; left valve with two compressed, ragged, recurved pseudocardinals, and two delicate laterals; right valve with one pseudocardinal, a minute one above it and a single lateral; beak cavities and muscle scars shallow, nacre bluish-white, silvery and somewhat iridescent behind, slightly thickened in front. The male and female shells are much alike, the latter being more inflated and a little fuller at the extreme post-basal region. The male shell is usually evenly rounded behind, that of the female is often a little truncate and sometimes has a blunt point above.  The greatest diameter is behind the center of the shell, and the female is remarkable for sometimes having the diameter greater than the height” (Simpson, 2014; Mather, 2007).