Page:American Seashells (1954).djvu/121

Rh 1 to $1 3/4$ inches in maximum diameter, elliptical to almost round in outline, low to quite flat. Characterized by radial rows of small beads which sometimes may be crowded together to form tiny, rough riblets. Exterior greenish black. Interior glossy-white, younger specimens having a blue tint. Patch of brown on inside generally weak or absent. Edge of shell usually with solid, black-brown, narrow band. Occasional albinos are cream-brown or tan on the outside. Compare with A. scutum which is smooth and has a barred band of color on its under edge.

$1 3/4$ inch in maximum diameter, elliptical in outline; generally with a moderately high apex which is minutely hooked forward and which is placed $1/3$ back from the anterior end of the shell. The 15 to 25 moderately developed, coarse, radiating ribs give the edge of the shell a slightly wavy border. Color grayish with tiny, distinct mottlings of white dots and blackish streaks and lines. Inside white with faint bluish tint and with a large, usually even, patch of dark-brown in the center. Edge of shell with a solid or broken, narrow band of black-brown. Common. Do not confuse this species with A. scabra which does not have the “hooked-forward” apex and is not glossy on its internal brown patch. Compare also with persona.

1 to $1 3/4$ inches in maximum diameter, with characters much the same as those of digitalis, but differing in being smoothish, larger, often slightly higher, and in having a strong tint of blue or blue-black inside. I am inclined to believe that Pilsbry is correct in considering digitalis as a smaller, ribbed form of persona, despite the fact that recent workers place these two species in different subgenera. It is possible that colder waters allow the smooth persona form to express itself. The Mask Limpet is very common from Monterey north. It is an intertidal dweller where strong waves flush the rock crevices. It feeds mostly during the ebb tide and is more active during dark hours. The small southern subspecies, strigatella Carpenter, is about $1/2$ inch in size, dark gray-blue inside, and externally with a mass of intertwining or joining radial bars of brown on a bluish or gray-white background.