Protoconch 2,5 smooth shining whorls, a little depressed, merging gradually into adult sculpture. Teleoconch 4,5 flatly convex whorls. Sutures strongly impressed. Sculpture of strong, high, sharp axial ribs, 10 to each whorl, crossed by fine transverse white striae, about 25 on body-whorl, 9 on penultimate, ribs sharply serrated at intersections; whorls sharply shouldered and turreted, ribs recurved and scaly on top of shoulders, continued as thin sharp ridges to sutures. Umbilicus small and deep, partly covered by inner-lip callus, ribs continued over base into opening. Aperture widely elongate, contracted both ends, a short open siphonal canal, toothed posteriorly; columella straight with 3 strong oblique plaits; inner-lip recurved as strong callus on to body-whorl; outer-lip flared outwards anteriorly, sharply edged, 10 lirations extend from near lip well into aperture. Colour white, purple-brown on top of shoulders, two broad brown or purple-brown bands round body-whorl, narrow white band between; lower brown band has a darker edge adjoining white section; lip of aperture white, brown blotching within.
Dimensions. Holotype, length 28-13 mm (marked on holotype as 27-5 mm). Holotype is maximum length. Average size 18 mm x 12 mm.

Tryon states (1885: 80) "Cancellaria crenifera and several other allied species are probably only varieties of C. scalarina Lamarck", also that "C. scalarina Sowerby (= C. thomasiana Crosse) is a variety of C. scalarina Lamarck", with which remarks I concur. Deshayes' detailed description of the species (1830: 189) identifies it well, and the later descriptions by Sowerby (1855: 452) and Reeve (1858: fig. 25) of C. scalarina Sowerby (= C. thomasiana) both agree with Deshayes' description. A number of specimens examined from Japan and Philippine Islands agree well with Australian specimens from the wide area of distribution shown above, only a few minor differences being apparent, all of which are variable and merge with those from other localities. Queensland specimens tend to have a darker background colour than those from most other areas. This species can be separated from Trigonostoma scalariformis Lamarck by its wider umbilicus, more spinose sculpture, and narrower and sharper axial ribs.

Distribution. From 32 km N. of Delambre Island, Dampier Archipelago , northwestern Australia (20° 05' S., 117° 06' E.), across north of Continent in many localities, and south along Queensland coast to 77 metres (greatest depth recorded) off Moreton Bay (27° 22' S., 153° 39' E.). Subtidal to 77 metres. Widespread throughout the Indian Ocean, western Pacific Ocean and northwards to Japan.