Meretrix lyrata
The overall shape is trigonal ovate. The posterior margin is more pointed than the anterior; the anterior and ventral margins are rounded. Both the anterior and posterior dorsal margins are subconvex. The posterior half of the flank is slightly more inflated than the anterior. The valves are equal in size and shape (equivalve), and there is no gape when they are closed. Sculpture consists of rounded comarginal ribs. Ribs near the ventral margin may be split; splitting causes more ribs to be present at the posterior than the anterior. The lunule is lightly impressed, extends 3/4 of the anterior dorsal margin and is defined by a fine shallow groove. The commissural margin is slightly raised at the center of the lunule. The umbo is slightly anterior, and the beaks also point slightly to the anterior. The escutcheon is not well defined.
The exterior color is light tan to light brown. The posterior dorsal margin may be a dark brown color. The interior is white with a purple or dark brown ray of pigment along the posterior dorsal margin.
The ligament is external, spans 1/3 of the posterior dorsal margin and is supported by nymphal ridges. On the left valve, there are three cardinal teeth. The anterior tooth (2a) is lightly bifid, the central tooth (2b) is not bifid, and the posterior tooth (4b) is not bifid and fused with the nymphal ridge. There are very fine vertical crenulations in the shallow groove between the nymph and appressed tooth. There is also one anterior lateral tooth (A2) on the left valve. On the right valve, there are three cardinal teeth. The anterior (3a) and central (1) teeth are not bifid; the posterior tooth (3b) is bifid. There are fine vertical crenulations on the ventral side of the nymph. There are also two anterior lateral teeth (A1, A3), as well as a very fine ridge running parallel to the posterior dorsal margin on the right valve. The posterior adductor muscle scar is rounder than the anterior adductor muscle scar. The pallial sinus is shallow.