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1 to $1 1/2$ inches in maximum diameter, elliptical in outline, with a moderately high apex which is placed $1/3$ to almost $1/2$ way back from the anterior end. With about 25 axial, weakly developed, radial ribs. Edge of shell slightly wavy. External color of strong black radial, often intertwining, stripes on a whitish cream background. Interior usually faint bluish white, with or without a dark-brown spot. Inner border edged with alternating black and cream bars. A common rock-dweller.

1 to $1 1/2$ inches in maximum diameter, almost round in outline, rather high, and smoothish. The northern subspecies, cribraria Gould (pl. 18w), found from Alaska to northern California, has interior with various shades of glossy, chocolate-brown, and with a narrow, solid black border. The exterior is plain dark-gray. The typical southern fenestrata Reeve (pl. 18t), found from Point Conception south, has an external color pattern of regular dottings of cream on a gray-green background. Its interior has a small, brown apical spot surrounded by a bluish area and bordered at the margin of the shell with brown. Intergrades occur near Point Conception. This species is the only Pacific Acmaea which lives among loose boulders that are set in sand. It only feeds when submerged. Common.

$3/4$ inch in maximum diameter. Shell low, and like A. scabra, is with distinct but widely spaced, radial ribs. Distinguished from scabra by its glossy, smooth interior which often has an evenly colored brown center. A. scabra has a rough interior center and the brown stain looks smeared. However, this species may be a form of scabra. It is very abundant south of La Jolla and is found with A. scabra and A. digitalis.