Shell of medium to moderately large size, up to 65.5 mm. (2,5 inches) in length, polymorphic, extremely variable in shape, altitude and colour pattern. Typical form ovate, depressed, with the apex at about the anterior fourth; sculptured with 20 to 25 narrow, slightly raised primary radials, and a varying number of very weak radial threads in the interspaces, but often, the latter are subobsolete; the whole sur¬face crossed by weak, but exceedingly dense, concentric lirations. Colour of exterior greyish buff, with a reddish brown pattern of interrupted radial lines and transverse streaks; interior yellowish, with the external brown markings showing through strongly; spatula ill-defined, fawn to chestnut-brown. Radula: Formula 3 + 1 + (1+0+1) + 1 + 3. There is a pair of strong centrals, each with a long lanceolate cusp, set tangentially to the shank, and in between these two teeth is a small, narrow, vestigial median plate; the pair of laterals are similar but have a broadly triangular base, and the lower cutting edge of the cusp is indented to form two denticles; all three marginals are present but they are very thin and semitransparent; only the inner one bears a slight cusp, and below these, joined by a thin membrane are three shorter narrow plates, the effect being of long and short marginals in a vertical alternation. Length: 19-66; Width: 15-55; Height: 3- 24 mm.

Shell ovate, depressed, thin but solid, slightly narrower in front. Surface sculptured with decidedly separated narrow radiating riblets, 20 to 25, having a number of smaller riblets (sometimes obsolete) in each interval, and decussated by fine crowded growth-striae, also often obsolete, but usually cutting the surface just in front of the apex into fine granules. Colour bluish-white, usually buff around the apex, striped in a divaricating pattern, or irregularly blotched and rayed down the ribs with brown or olive. Apex not prominent, at the anterior fourth or fifth. Interior buffish-olive, with a silvery lustre, showing the colour-markings of the outside, having a white or brown central callus, often ill defined. (Pilsbry.)
Length, 44 mm.; breadth, 34 mm.; height, 8 mm. (typical form).
Hab.—Throughout New Zealand, but more common on the east coast of the North Island.
Remark.—This also is a very variable shell, especially in the colour-

This is the most common of the New Zealand limpets and the most variable, not only in shape and sculpture, but also in colour pattern. The many forms of the species are outlined in the following formal description. In general, north¬ern shells, which are the typical form, have the primary ribs coloured brown, and there is often a connecting pattern of transverse streaks (the earlii pattern). Most southern shells, on the other hand, have the sculpture finer, more even, the external markings indistinct, and internally there is a greenish silvery to golden lustre. This, the perana form, is the dominant one at Stewart Island and the southern part of the South Island, but it is known to occur also on the west coast of the North Island at Whitecliffs, north Taranaki, and also at the Three Kings Islands. On the other hand, at Cape Foulwind on west coast of the South Island both the perana and earlii forms occur together. The earlii pattern, which is more common in northern shells, is essentially a juvenile one, and seldom persists into the fully adult, without resolving into radial streaks, more or less confined to the primary radials.
Thomson (1919), in his paper on polymorphism in Cellana radians was of the opinion that colour pattern changes in the fully adult of this species were due to external erosion, accompanied by a compensating internal build-up of callus. In such senile examples only deep-seated colour, associated with the primary radials still persists.

New Zealand: North, South and Stewart Islands.