Shell small to moderate sized, up to 48 mm. (almost 2 inches) in length, but usually between 24 and 28 mm., solid, normally high-conical, with the apex at about the anterior third. Sculpture consisting of eleven strong, primary, radial ribs, each interspace with a central nodulose secondary radial, flanked on each side by a pair of much weaker radials; the whole crossed by dense concentric threads, that thicken like knots, wherever they surmount the primary and secondary radials. Colour of exterior: the primary ribs pale lilac-grey, the interspaces dark purplish brown to almost black, with the nodes on the secondary radials picked out in white. Color of interior: with broad, dark purplish brown rays and silvery intermediate narrow rays; spatula dark chestnut-brown to almost black, often partly clouded with greyish callus. Radula: Formula (3) + 1 + (1+0+1) + 1 + (3); similar to the radula of radians, the paired centrals each with a long lanceolate cusp, set tangentially to the shank, and the laterals similar but heavier,, with the lower edge indented to form two denticles; the three marginals are fused into a small irregularly-shaped, semitransparent plate, without cusps. Length: 22-48 mm; Width: 18,5-44,5 mm; Height: 7-21 mm.

Shell solid, oval or oblong, low conical. Sculpture consisting of larger radiating coarsely nodular ribs, about 11 in number, with, a somewhat smaller rib between each pair of larger ones, the intervals radiately striated ; growth-striae fine, often quite distinctly cutting the radial striae. The larger ribs are light, the intermediate ribs are black dotted with white, especially in the young, this colouring being less obvious on large shells. Apex at about the front third, erect. Interior having alternating silvery and black rays, the latter usually 11 in number ; the large central area black, suffused more or less with cream colour in the depth of the apex. (Pilsbry.)
Length, 32 mm. ; breadth, 25 mm ; height, 10 mm. Hab.—Throughout New Zealand, but more common in the south.
Remark.—This species is very well characterized, and does not show any very great variability, except that the apex is sometimes quite anterior.

In its young non-eroded state this species has a most attractive colour pattern, the primary ribs being lilac-grey, and the intermediate areas purplish brown to black, with the nodes picked out in white. In large-sized examples the exterior is almost invariably eroded and little of the basic colour pattern remains. Also, in coastal areas subject to rigorous wave action, the profile is low, and the shape varies from elongate-ovate to broadly-ovate. This species is common on rock faces in the upper tidal zone.

New Zealand: North, South and Stewart Islands.