Shell reaching a large size, up to 83 mm. (3,25 inches) in length, but usually be¬tween 45 and 60 mm., solid, but not massive, narrowly ovate, with a subcentral nucleus, and conical with straight sides. Sculpture consisting of from 46 to 50 bold, sharply raised, flat-topped radials, that are smooth, except were crossed by weak concentric growth striae; margin shallowly corrugated to deeply indented by square-cut crenulations. Colour of exterior consisting of plain black radial ribs, with grey or whitish interstices, the apical area only, tessellated with black and white dashes; internally silvery to bluish-leaden, with the dark ribbing showing through; spatula leaden to solid black, but often partly or completely white callused. When the shell is eroded externally that surface becomes whitish or cream coloured, and the corresponding interior is usu-ally diffused with yellow or orange-brown. Length 42-83 mm; Width 32-68 mm; Height: 12-40 mm.

Cellana exarata (Reeve, 1854). (Synonym: Patella undatolirata Reeve, 1854; Helcioniscus exaratus Nuttall, Dall, 1871.) Length, 40 mm; diameter, 40 mm; height, 17 mm. Shell: conical, slightly broader posteriorly than anteriorly; apex subcentral. Sculpture: close-set radiating ribs interspersed with finer ribs; ribs not projecting beyond shell margin. Color: dark gray, ribs usually black; interior blue-white; spatula gray or black. Animal: foot and mantle gray or black.
C. exarata is found on basalt shorelines from the spray zone where it occurs with the nerite, Nerita picea, and the algae Ahnfeltia, Rhizoclonium, and Ulva seaward to the calcareous algal zone where it intermingles with C. sandwicensis and the sea urchin Colobocentrotus atratus. Correa (1969) suggests that rapid movement and the ability to raise the shell and ventilate the mantle cavity are both factors which enable this species to live in a more fluctuating environment than does C. sandwicensis. In the higher regions of its distribution, the opihi have fixed home scars, indicated by clusters of animals which persist from month to month on boulders, and by grazed areas around the shells. The scars are not deep as they are in patellids elsewhere, but are merely grazed sections of the substrate.
The sexes are separate, fertilization is external, and the nonfeeding larvae may settle in three or four days after fertilization (Helfrich, 1971). The limpets settle at about 1 mm in length, and grow at rates of about 5 mm per month until they are mature (about 25 mm in length), when growth slows to about 2 mm per month. Spawning probably occurs primarily about December and January and recruitment is most noticeable from March to June.
C. exarata has been recorded as far north as French Frigate Shoals in the leeward islands where it is found on La Perouse Pinnacle, but not on the calcareous shoreline of the atoll itself.

Dr. Alison Kay (1969, pp. 1, 2) advocated separation of exarata into three distinct species.
(1) exarata: Shell black, finely sculptured, the radial ribs not extending beyond the margin; foot of animal dark grey, mantle almost black; mantle appendages short, extending only 5 mm. beyond the edge of the shell.
(2) sandwichensis: Shell black, coarsely sculptured, the radial ribs extending beyond the margin; foot of animal yellow, mantle grey; mantle appendages long, some extending 20 mm. beyond the edge of the shell.
(3) melanostoma: Shell cream or white, with brown ribs; foot of animal and the mantle bright green.

Hawaiian Islands. It belongs to the splash zone, on the islands of Oahu, Molokai, Maui and Hawaii.