Truncilla truncata shell description:

“Shell subrhomboid, solid, inflated, with a very sharp posterior ridge, behind which it is decidedly truncated; beaks high and full, turned forward over a small lunule; region of the beaks and upper part of the shell decidedly flattened; central base of the shell full; posterior point sharp, elevated considerably above the base; surface with irregular, subsulcate growth lines; epidermis dull or somewhat shining, often having wrinkled loops behind, yellowish-green with numerous wavy, often broken rays.  Sometimes in addition to the rays there are numerous wavy or zigzag lines and occasionally the shell is tawny or reddish and rayless; hinge line curved; pseudocardinals ragged, two in the right valve and one in the left, sometimes they are much split up; left valve with two laterals; right valve with one and sometimes a faint second one below it; beak cavities not deep; muscle scars impressed; nacre bluish-white, white, salmon or reddish.  The form of the shell is quite variable and those of the female and male differ but little from each other.  The female shell is a little more produced at the central base" (Simpson, 1914; Mather, 2007).