The following description of the Slabside Pearlymussel is taken from Parmalee and Bogan (1998, p. 150-152), Williams et al. (2008, p. 589-591), and Schilling (2015, p. 82). The Slabside Pearlymussel is a moderately sized mussel that reaches about 9 cm (3.5 in) in length. The shape of the shell is subtriangular, and the very solid, heavy valves are moderately inflated (Figure 2.2). Shell texture is smooth and somewhat shiny in young specimens, becoming duller with age. Shell color is greenish yellow, becoming brownish with age, with a few broken green rays or blotches, particularly in young individuals. Internally, the pseudocardinal teeth are triangular or blade-like in shape. The lateral teeth are slightly curved, with two in the left valve and one in the right valve. The color of the nacre is white, or rarely, straw-colored. Most anatomical features are tan or brown and vary from rusty orange to shades of reddish or grayish brown. Only a few select features will be detailed, but further information of soft anatomy is described by Williams et al. (2008, p. 590). The mantle is tan to light brown or golden and sometimes orange, and often has orange outside of the pallial line; the visceral mass (collective assemblage of internal organs) is creamy white to tan and often has an orange cast; the foot is bright orange or rarely white; and the gills are creamy white to light brown, gold, or orange. The gills are only connected to the visceral mass anteriorly; the outer gills are marsupial, holding glochidia (larvae) in short folds when gravid.