ACM.EA. 21 



" They present nearly every variation in form, from wide, oval and 

 nearly flat, to narrow, triangular, high and very compressed. The 

 extreme apex is almost always black. It is usually furnished with 

 a few dark brown stripes, radiating from near the apex but seldom 

 reaching the margin in adult specimens. These however are want- 

 ing in some specimens. In all its forms it is a well marked species 

 and cannot be united with any now known from the California coast. 

 Dr. Carpenter proposes to rename this form specifically " casta " and 

 to apply the term triangularis to the compressed variety only ; it is 

 doubtful, however, if such a course would be admissible, as every 

 transition in form can be observed in a very few specimens. (Dall.) 



Typical triangularis is shown in figs. 77, 78. An example meas- 

 ures: length 6|, breadth 3, alt. 4 mill. 



The form called CASTA is illustrated by figs. 74, 75, 76. This is 

 really the normal form of the species, the other being modified by 

 the narrow frond supporting it. A large example measures : length 

 12, breadth 9, alt. 4 mill. 



Var. ORCUTTI Pilsbry. PI. 42, figs. 84, 85, 86. 



Has the oval base of A. casta, but the apex is decidedly anterior, 

 as in A. persona. Surface lusterless, having rather rude growth- 

 lines and very obsolete, low, wide radiating riblets, some at wide inter- 

 vals slightly more prominent. Color white, or tinged with cream or 

 green ; apex obtuse, eroded, but around the eroded area there are 

 brown dots, indicating that the young were marked like A. casta. 

 Interior white or fleshy-cream tinted, sometimes with slight greenish 

 or brown stains in the cavity ; border wide, darker than the rest of 

 the interior. Length 11?, breadth 9, alt. 5i mill. 



San Diego, California. 



Specimens of this curious variety were received from Mr. C. R. 

 Orcutt. It has the coloration of some specimens of A. triangularis, 

 but the form recalls A. persona. 



A. ROSACE A Carpenter. PI. 7, figs. 71, 72, 73. 



Shell small, conical, thin, smooth or with very obsolete ribs. The 

 young are pale roseate, with few white and brown subradiating 

 spots ; the adults have rosy brown and whitish streaks or are dotted 

 with pale rose. Apex elevated, a little anterior ; inside white or 

 rosy. Length 8, breadth 6i, alt. 3? mill. 



San Diego to Monterey, California. 



