Shell moderately large to large (normal length: about 40 to 65 mm), smooth, with a straight to very slightly convex profile. The spire is low to moderately high, with a straight to slightly convex profile. The shoulder is clearly angulated. The shell is pale purplish-brown, with dark brown crescent shaped flammules on the spire. The aperture is white in the larger specimens and has a faint violet shading in the smaller ones. Radula: Vermivorous type, long and narrow. The apical portion is longer than half the length of the radular tooth. Blade prominent, far from the ill-defined waist. Barb rather long and well parted. One row of denticles in the serration. Base narrow.

C. ambiguus Reeve, 1844 can be separated from C. tabidus Reeve, 1844 by its normally larger size and angulated shoulder (it is rounded in C. tabidus Reeve, 1844). C. bellocqae van Rossum, 1996 has a different profile and pattern.

Geographical distribution: Known from Senegal (South of Dakar), Gambia and probably northern Guinea-Bissau also. Absent in the Cape Verde Islands.