20 ACM^EA. 



Inside bluish-white, showing the color pattern of the outside 

 through the shell. Length 11, breadth 4, alt. 3 mill. 



Santa Barbara, Monterey, San Diego, California. 



Patelloida depicta HINDS, Ann. and Mag. N. H. x, p. 82, t. 6, f. 

 4, 1842. ^Collisella f depicta DALL, Amer. Journ. Conch, vi, p. 254. 



Resembles no species but A. paleacea. The long narrow form is 

 caused by growth on Zostera fronds. There is some variation in the 

 coloring, broad bands sometimes replacing the narrow lines. The 

 front end is generally of a decidedly darker shade. A specimen of 

 average proportions is figured. 



The form of this species as developed when growing on a flat sur- 

 face instead of a narrow frond, is shown in fig. 41 of pi. 6 drawn 

 from a specimen in the Smithsonian collection. It measures, length 

 6, breadth 4?, alt. H mill. Sculpture and coloration are as in the 

 type. 



A. PALEACEA Gould. PL 6, fig. 42. 



Shell small, thin, long and narrow 7 , parallel sided ; apex near the 

 front end. Surface sculptured with close radiating riblets. Color 

 yellowish-brown, darker toward the margins and on the front slope. 



Length 7, breadth H, alt. 2 mill. 



Monterey, Santa Barbara and San Diego, California. 



A. paleacea OLD., Mex. and Cal. Shells p. 3, t. 14, f. 5. CPR., 

 P. Z. S. 1856, no. 40. Collisella paleacea DALL, Amer. Journ. 

 Conch, vi, p. 253 (dentition). 



Smaller and narrower than A. depicta, the surface radiately ribbed 

 and not variegated. The sculpture is quite distinct under a lens of 

 moderate power. 



A. TRIANGULARIS Carpenter. PI. 7, figs. 74-78. 



Shell small, rather thin, either oval or narrow and parallel-sided ; 

 elevated, apex subcentral, a trifle recurved ; surface nearly smooth, 

 but showing very fine radiating stride under a lens. Color pure 

 white, sometimes immaculate, but usually having 6 or 7 wide brown 

 rays, which usually do not extend to either apex or basal margin. 

 There is almost always a brown spot just behind the apex. Inside 



pure white. 



Monterey and Baulinas Bay, California. 



Nacella (f paleacea, var.} triangularis CPR. Proc. Cal. Acad. Sci. 

 iii, p. 213, 1866. Collisella (7) triangularis DALL, Am. Jour. Conch, 

 vi, p. 254. Nacella .casta CPR. olim. 



