Callista eucymata
The overall shape is subtrigonal, ovate. The anterior and ventral margins are rounded, and the posterior margin is subtruncated. The anterior dorsal margin is nearly straight, and the posterior dorsal margin is subconvex. The valves are inflated, equal in size and shape (equivalve), and there is no gape when they are closed. Sculpture consists of growth lines and wide, rounded comarginal ribs. There are no ribs on the lunule; it is spear-shaped, defined by a fine shallow groove and extends half the anterior dorsal margin. The umbones are prominent and subanterior, and the beaks also point slightly to the anterior. The escutcheon is not well defined.
The exterior is white with red-brown blotches, tent marks, and/or radial stripes. The blotches and tent marks may form radial stripes. The lunule is typically partially covered with red-brown coloration. The interior is white with a posterior ray of purple pigment.
The ligament is external, extends half the posterior dorsal margin and is supported by nymphal ridges. On the left valve, there are three cardinal teeth (2a, 2b, 4b), none of which are bifid. The anterior (2a) and central (2b) teeth are united dorsally, forming an inverted "v" shape. The posterior tooth (4b) is fused with the nymph. 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, and the posterior tooth (3b) is bifid. There are two anterior lateral teeth (A1, A3) on the right valve, as well as a fine, weak ridge that runs parallel to the posterior dorsal margin. The anterior and posterior adductor muscle scars are similar in size and shape. The pallial sinus is rounded and extends to the middle of the hinge plate in length.