Circe quoyi
Similar to Circe plicatina. Circe quoyi is distinguishable by its thinner ribs that are of equal strength throughout the surface of the flank.
Similar to Circe scripta. Circe quoyi has wider, more largely spaced comarginal ribs and its oblique ribs at the anterior and posterior meet in the central area of the nepioconch; the oblique ribs of C. scripta do not extend to the central area.
The overall shape is trigonal ovate. The posterior margin is slightly truncated. The anterior and posterior dorsal margins are nearly straight. The valves are variable in inflation, and they are equal in size and shape (equivalve). There is no gape when the valves are closed. Sculpture consists of growth lines and comarginal ribs that become stronger and then weaker as the animal grows. There are also oblique ribs at the anterior and posterior areas of the flank that are most prominent at the nepioconch. The intersection of the comarginal and oblique ribs results in weak nodules at the anterior and posterior of the nepioconch. The lunule is not impressed; it is elongate in shape, defined by a fine shallow groove and extends 1/3 of the anterior dorsal margin. The umbo is central and the beaks point slightly to the anterior. The escutcheon is not well defined.
The exterior is white or light tan. There may be light brown pigmentation along the comarginal ribs or a dirty gray periostracum. The lunule and escutcheon may be marked by dark brown coloration. The interior is white with pink or purple coloration concentrated at the pallial line and/or the posterior margin.
The ligament is external, but sunk beneath the flank of the shell; it is supported by nymphal ridges. The hinge plates on each valve are elongated vertically. The left valve has three cardinal teeth (2a, 2b, 4b), none of which are bifid. The posterior tooth (4b) is fused with the nymph, and the central tooth (2b) is trigonal in shape. 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 lightly bifid. There are also two anterior lateral teeth (A1, A3) on the right valve. The posterior adductor muscle scar is slightly larger and more elongate than the anterior. The pallial sinus is absent.
Circe quoyi is found in central Western Australia to South Australia (Lamprell 1992).