Shell minute, thin, semitransparent when fresh, planorbiform, of few convex whorls, nearly symmetrically coiled, forming a concavely depressed spire and large umbilical cavity. Epidermis thin, nearly colourless. Nuclear whorl relatively large, smooth, turned downward, seen only in a basal view, leaving a small pit above. Suture deep and channelled. Aperture triangular-ovate, expanded below, angulated above, with a relatively wide deep sinus just below the suture. Peritreme thin, simple, continuous, not modified, slightly attached. The operculum is very thin, almost colourless, broad-ovate, with the nucleus below the centre and represented by a small smooth space indefinitely defined by an indistinct line ; from this arise numerous raised lines in the direction of the lines of growth, which are at first near together, but diverge toward the outer margin, where they terminate just within the edge; others arise between these, about two-thirds their length.
Distribution.—The type is from about 16 fathoms, off Cape Hatteras, North Carolina. A second species, C. californica, Bartsch, has been recorded from the California coast.