Shell solid, elongate-oval, of 7 whorls, including a blunt brown protoconch of 2 convex smooth whorls. Spire-whorls convex in the upper half, nearly straight in the lower. Suture distinct, very narrowly tabulate. Base moderately roundly contracted. Aperture elongate-oval. Outer lip simple, thin, profile slightly sinuous, with numerous spiral plicae in the throat. Columella nearly straight, slightly cut away to the left in front, with four stout oblique plaits; notch with a narrow reflected edge. Wide, round, low axial ribs, much wider than the interspaces, thirteen in the penultimate, undulating the suture, vanishing on the base of the body-whorl and towards the aperture. Articulated with infrasutural large irregular blackish-brown blotches, about nine in the body-whorl; and with two similar approximate spiral rows, the upper the larger, winding round the base from the back of the aperture, below which are dark maculations. A spiral of close-set axial, narrow, brown hair-lines covers the lower third of each spire-whorl, and runs between the two rows of larger articulations on the body-whorl.
Dim.—Length, 12 mm.; body-whorl, 625 mm.; width,
5 mm.

Locality.—Type, beach Petrel Bay, St. Francis Island many; MacDonnell Day, rare.
It is named after Master Francis Arnold, of St. Francis Island, who was of great help to me when collecting on that island, made historic by the visits of Matthew Flinders and Mons. Baudin.