Mitra semigranosa: Shell 46 mm (about 2 inches) in length, elongate-ovate and solid, sutures distinct and slightly adpressed on the body whorl. Whorls 6 apart from the protoconch which is missing; postnuclear whorls with axial riblets and 4 overriding spiral threads which produce horizontally elongated, narrow beads upon the ribs. The beaded sculpture disappears on the second half of the penultimate whorl and is replaced by fine and numerous spiral striae; striae number about 20 on the penultimate and about 30 on the body whorl in addition to a dozen oblique cords at the base. The body whorl has obsolete and ill-defined axial threads which resemble growth-striae. Aperture slightly longer than the spire, moderately open and smooth within, outer lip moderately thickened and simple, regularly convex; columella cal¬loused, thinned on the parietal wall but with a small callus-pad near the juncture of the aperture, columella with 4 strong, oblique folds. Siphonal fasciole straight, siphonal notch distinct. Uniformly brown in colour, sutures slightly paler, aperture white but margined with brown, columellar folds white.

Mitra semigranosa: This is a rare species which is lacking in museum collections. It is closely related to the common M. orientalis but has a more granulose sculpture on the spire whorls which may persist to the penultimate whorl. The description is based on the holotype which was collected devoid of animal and lacks the periostracum which is probably present in living specimens.

Mitra semigranosa: Ecuador to Chile.