ACMAEIDAE 103 



I to 1% inches in maximum diameter, elliptical to almost round in out- 

 line, 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 



Plate i8f 



Aleutian Islands to Socorro Island, Mexico. 



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 



Plate i8q 



Aleutian Islands to Monterey, California. 



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 



Plate 1 81 



Vancouver, B.C., to Lower California. 



