Shell subquadrate, rather thin, much inflated, slightly excavate on the posterior side, which is bounded by an obscure angle, posterior margin truncate, anterior rounded, ventral straight, dorsal curved. Colour olive-buff. Sculpture fine, close, con¬centric threads. Umbo prominent, incurved. Two cardinal teeth in each valve. Length, 25; height, 23; depth of single valve, 9 mm.
Hab. : A few separate valves from the beach at Karumba, Gulf of Carpentaria (self, 1903). This is a deeper, squarer shell than C. oblonga Hanley, and is somewhat of the same proportions as C. sphaericula Desh., than which it is larger and more solid.