Shell up to 28 mm (about 1,25 inches) in length, elongate-ovate to ovate, solid, sutures distinct, narrowly channeled and finely crenulate. Whorls 5-7, apart from an eroded white protoconch, spire whorls weakly convex, sculptured with shallow and smooth spiral grooves which number from 3-7 on the penultimate whorl; on the body whorl the first 3-6 spiral grooves are confined to the shoulder, the centre is usually smooth, and towards the base there are 2-5 grooves winch are followed by up to 10 oblique cords. The aperture is longer than the spire, narrow but slightly widening anteriorly, smooth within; outer lip prominently thickened, interior callosity either prominent or almost absent, margin of outer lip smooth. Columella calloused anteriorly and with 4-5 strong, oblique folds, parietal wall glazed, posteriorly with a thin callus; siphonal fasciole short and straight, siphonal notch prominent. Uniformly dark tan in colour, occasionally with slightly paler axial streaks, ornamented with obsolete, faint brown spiral lines which are obscured on the body whorl but become apparent on the back of the outer lip and continue as spots or short lines onto the white calloused margin; aperture and columella white, parietal wall white but edged with brown. Periostracum thin, dark brown and moderately opaque.

The species is easily recognized by its uniformly horny-brown colour, minutely crenulate sutures, white aperture and fine, short brown lines on the edge of the outer lip. This species has been usually known under the names oi M. fuscescens (Pease) or M. brunnea (Pease), but Reeve's name M. fastigium has chronological priority.

East Africa to Polynesia and the Hawaiian Islands. On reefs, under rocks and coral and in crevices, in the intertidal zone.