Shell of moderate size, averaging about 35 mm, but reaching 47 mm. (1 3/8 to 1 7/8 inches) in length, solid, tall-conical, with the apex varying between subcentral and the anterior fourth. Sculpture extremely variable, ranging from low, rounded, primary radials with 4 to 6 radial threads in the interspaces (typical form), to strongly sculptured shells with about 24 bold carinated and spinose primary radials, with a few relatively strong interstitial radials (forma squamifera). Colour, externally yellowish brown with the radials paler, interior porcellanous-white with a faint yellowish brown spatula. In the typical peronii form the secondary radial interspaces are often lined in black. Shell margin thin semitransparent, yellowish with the external interstitial lines showing through. The shell margin varies according to the strength of the external sculpture being almost smooth in the peronii form but strongly corrugated in the squamifera form. Radula—Formula 3 + 1 + (2+1+2) + 1 + 3. Central teeth five, the middle one much smaller than the other four, lateral with four cusps, followed by the usual three functionless marginal.
Length: 31,5 – 47 mm. Width: 25 – 39 mm; Hight: 12,5 – 25 mm

This species is extremely variable in shape and in sculptural development, ranging from typical peronii, which is weakly but regularly smooth ribbed, thus producing an almost smooth margin, to the strongly squamose sculptured squamifera form, in which the margin becomes noticeably corrugated. Dr. Hope Macpherson (1955) claimed that when large series were examined, both forms were seen to intergrade, and no differences in the radula were apparent. Common on exposed rock platforms of the lower littoral zone to the sublittoral fringe, among holdfasts of giant kelp.