ACMAEIDAE 105 



V2 inch in maximum diameter, very narrow, 3 times as long as wide. 

 Sides straight with brown verti(?al stripes on a whitish background. Smooth- 

 ish. This species is found on the broad-leaved eel-grass of the estuaries. Abun- 

 dant in certain localities, such as Mission Bay. 



Acmaea instabilis Gould Unstable Limpet 



Plate i8zz 



Alaska to San Diego, California. 



I to I M inches in maximum diameter, oblong with a rather high apex. 

 Sides compressed. Lower edge curved so that the shell rocks back and forth 

 if put on a flat surface. Exterior dull, light-brown. Interior whitish with 

 faint brown stain in the center and with a narrow, solid border of brown. 

 Inhabits the stems or holdfasts of large seaweeds. Moderately common. 



Acmaea insessa Hinds Seaweed Limpet 



Plate i8z 



Alaska to Lower California. 



/{> to % inch in maximum diameter, narrowly elliptical, with a high apex, 

 and colored a uniform, greasy light-brown. Abundant on the stalks or hold- 

 fasts of the large seaweeds, such as Egregia. 



Acmaea pale ace a Gould Chaffy Limpet 



Vancouver, B.C., to Lower California. 



% inch in maximum diameter, very fragile, translucent-brown, 3 or 4 

 times as long as wide. Sides straight with fine, raised radial threads. Abun- 

 dant on the narrow-leaved eel-grass of the open coast. 



Atlantic Coast Species 

 Acmaea testudinalis testudinalis Miiller Atlantic Plate Limpet 



Arctic Seas to Long Island Sound, New York. 



I to 1% inches in maximum diameter, oval in outline, moderately high 

 with the apex nearly at the center of the shell. Smoothish except for a few 

 coarse growth lines and numerous, very fine axial threads. Interior bluish 

 white with a dark- to light-brown center and with short, radial brown bars 

 at the edge. Exterior dull cream-gray with irregular axial bars and streaks of 

 brown. A common littoral species in New England. Formerly referred to 

 as A. tessulata Miiller. The fomi alveiis Conrad is a thin, elongate, heavily 

 mottled ecological variant which lives on eel-grass. 



