Cavolinia tridentata occidentalis, Dall, 1908
Diagnostic description:
Smallest forma of the species, resembling that of Cavolinia uncinata. Dorsal surface is strongly vaulted with three moderately developed central and two faintly developed lateral dorsal ribs. Upper aperture lip is rounded without keels along the lateral sides. Ventral side is strongly vaulted, and is perfectly round in profile view. Aperture triangular-lunar shaped. Growth lines with up to 20 transversal striae on ventral surface. [van der Spoel, 1976]