Shell up to 25.0 mm (1 inch) in length, variable in form, elongate-ovate to cylindrically-ovate, spire occasionally acuminate but generally blunted through the erosion of the spire whorls, spire short, sutures distinct hut narrowly incised. Whorls 5-6, apart from an eroded protoconch, spire whorls regularly convex, sculptured with very fine, shallow and minutely pitted spiral lines or grooves which number from 4-7 on the penultimate and from 10-25 on the body-whorl, apart from 8-12 weak, oblique cords at the base; in many individuals the spiral grooves become obsolete on the centre of the body whorl, while in some small, mature specimens the spiral grooves may he deeper and produce weak spiral threads, under magnification, flue, longitudinal hair-lines are discernible. Aperture longer than the spire, very narrow and smooth within, outer lip thickened, concave near the start and swelling into the aperture, callus weak and appreciably less prominent than in M. auriculoides, margin of outer lip with 8-15 small crenulations which ex-tend from the interior callus to the base. Columella calloused anteriorly and with 4-5 oblique folds, parietal wall only glazed and posteriorly with a weak callus or calloused denticles; siphonal canal short and straight, siphonal notch moderately distinct. Reddish-brown to chestnut-brown in colour, ornamented with either a narrow or moderately broad, white or yellowish spiral band anteriorly to the suture on the body whorl, and a single, interrupted band of the same colour adjoining sutures on the spire whorls; this spiral band is frequently blotched with white or pale yellow, and on the lower half of the body whorl are small, white spots. On reaching the hack of the aperture, the peripheral hand on the body whorl erupts into an irregular and somewhat smudged blotch which extends upward from the band. Aperture, anterior columellar callus, folds and parietal thickening white, bluish white or light violet, parietal wall brown. Periostracum thin, orange-brown and moderately translucent.

This species is the S. auriculoides of authors but not of Reeve, and differs from S. auriculoides in its longer body whorl, more slender and usually more cylindrical form, slight constriction near the siphonal canal, less inflated body whorl, weak interior callus on the outer lip, and the margin of the outer lip is minutely crenulated along its entire length. In S. assimilis, the white presutural band on the body whorl errupts into a large, smudged blotch on the back of the outer lip, a feature not observed in S. auriculoides.

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