14 ACM^EA. 



Interior porcelain-white or blue-tinted, with sometimes a few faint 

 spots of brown in the cavity. Inside border transparent-yellowish 

 or showing faint brown markings.) 



Length 37, breadth 31, alt. 7-8 mill. 



Vancouver's Island to Acapulco, western Mexico. 



Patella scabra Rv., Conch. Icon. f. 119. Acmcea scabra CPU., 

 Am. Journ. Conch, ii, p. 340. Collisella scabra DALL, 1. c., vi, p. 

 251, t. 14, f. 12, 12a (dentition). Acmcea (scabra var.?} morchii 

 BALL, Proc. U. S. Nat. Mus. 1878, p. 47. 



The typical form is easy to recognize by its light coloration and 

 the jine rasp-like riblets of the surface. Forms in which the outer 

 layer of the shell is deep brown instead of buff, and the inside bor- 

 der consequently blackish, are quite similar to some variations of 

 A. patina ; but sculpture and color-pattern will usually permit one 

 to separate them readily. 



Two forms have been described : 



Var. LIMATULA Cpr. PI. 3, figs. 38, 39, 40. 



Outer layer of the shell black, covered with an olive-green, or 

 sometimes light bluish, epidermis ; inside border black ; a deep 

 brown central spot. Distribution mainly southern, San Diego to 

 Acapulco. 



A very beautiful color-pattern is shown in figs 45, 46, drawn from 

 San Diego specimens. White rays alternate with dark olive. 



As an extreme form of this variety, Var. MORCHII of Dall (pi. 3, 

 figs. 47, 48, 49), must be ranked. It is typically much elevated, the 

 apex subcentral and curved forward, sculpture coarse. Otherwise 

 like var. limatula. Locality, Tomales Bay, Luw^r California. The 

 large suite of shells before me from Tomales Bay show every inter- 

 mediate stage between the high, cap-shaped forms and the normal 

 limatula. The former constitute a peculiar phase of development 

 attained by comparatively few individuals. Figures 47-49 are 

 drawn from Tomales Bay specimens. 



. 

 A. SPECTRUM Reeve. PL 1, figs. 7, 8, 9. 



Apex rather anterior ; slopes rather straight ; sculptured with 

 very strong close rough ribs, with smaller intervening riblets ; cen- 

 ter of the inside white, with dark spots and bars. 



Normally it is solid, rather depressed, with from 20-30 very 

 strong, rounded ribs not evanescent anteriorly, the interstices being 

 occupied by intercalary riblets. The color is white, with fine lines 



