Shell up to 37.0 nun (1,5 inches) in length, heavy and solid, ovate, sutures distinct, irregular and narrowly incised, spire short. Whorls 5, apart from the protoconch, spire whorls convex but usually eroded up to the penultimate or antepenultimate whorls, last 2 whorls smooth apart from obsolete spiral striae, macroscopic lon¬gitudinal hairlines and distinct cords on the lower half of the body whorl. Aperture longer than the spire, narrow and smooth within, outer lip gibbous and angulate near the start, greatly thickened, margin smooth, interior of lip prominently calloused. Columella concave, calloused, and with 4-5 prominent and curved folds, posterior of parietal wall with a white callosity, siphonal fasciole short and slightly angled towards the aperture, siphonal notch distinct. Almost black in colour, ornamented with 1 or 2 very narrow, orange, pale yellow or white bands on the body whorl; the narrow bands are brighter in parts, giving the band the impression of being spotted. The parietal wall is brown and the aperture, columellar folds and parietal callosity are bluish while. The periostracum is moderately thin, orange-brown, longitudinally striate and moderately opaque.

The centre of distribution of this uncommon species appears to be Micronesia, and the species rarity increases west and south of this region. We have not seen actual specimens east of Nine Island in the Pacific, but Dautzenberg and Bouge (1933) report the species from several localities in the Tuamotus. The species has been confused with M. scutulata (Gmelin) and M. colombelliformis Kiener. From the former species it differs prominently in form, the gibbous and calloused outer lip, and from the latter in being al¬most black in colour and ornamented with 1 or 2 narrow, spotted bands.

Cocos-Keeling Islands and Indonesia to Polynesia. On reefs, under coral, rocks and in crevices, in the intertidal zone.