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ACMAEIDAE 103
I to 1% 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.
Ac77mea digitalis Eschscholtz Fingered Limpet
Aleutian Islands to Socorro Island, Mexico.
Plate i8f
1% inch in maximum diameter, elliptical in outline; generally with a
moderately high apex which is minutely hooked forward and which is placed
Vz back from the anterior end of the shell. The 15 to 25 moderately devel-
oped, 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 v/ith 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.
Acmaea persona Eschscholtz Mask Limpet
Aleutian Islands to Monterey, California.
Plate i8q
I to 1% 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 H 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.
Acmaea scabra Gould Rough Limpet
Vancouver, B.C., to Lower California.
Plate 1 81