Mitra cookii: Shell up to 40 mm (about 1,5 inches) in length, elongate-ovate to fusiformly-ovate, slender and moderately light in weight. Whorls 6-8 apart from 1,5-2 nuclear whorls, sutures moderately impressed, spire whorls slightly convex. Moderately smooth in appearance, sculptured with fine, punctate spiral threads which number from 4-10 on the penultimate and up to 40 on the body whorl; the spiral threads are frequently confined to an area near the sutures and the anterior part of the spire whorls and centre of the body whorl are usually smooth. The base of the shell has up to 20 punctate spiral grooves or cords and the body whorl is constricted near the siphonal canal. Aperture slightly shorter or longer than the spire, narrow, smooth within; outer lip moderately thin, simple and regularly convex. Columella only weakly calloused and with 4-5 thin, oblique folds, siphonal notch weak. Dark brown to tan in colour, ornamented with pale axial streaks on the spire whorls and a light coloured central band on the body whorl; the pale transverse zone is occasionally bluish-white and fine axial lines intrude into this zone. The aperture and columella are brown, the folds are slightly paler.

Mitra cookii: This species is occasionally reported from southern Queensland, but specimens labelled "M. cookii" examined from this area, were the slender form of M. variabilis Reeve; the actual occurrence of the species in southern Queensland cannot of course be excluded. Although not previously reported from farther south than New South Wales, we have seen two records from South Australia. The species is intermediate in characters between M. carbonaria Swainson and M. variabilis Reeve.

Mitra cookii: Northern New South Wales to Yorke Peninsula, South Australia. Under rocks, in the intertidal zone.