FISSURELLA. . 143 



The animal of F.viresceiisSovtb. (belonging to the section Cremides) 

 is figured on pi. 61, figs. 13-15. The mantle-edge is fleshy and 

 papillose, broad. The upper surface of the foot is longitudinally 

 wrinkled and sparcely granose ; epipodial row of papilla? extending 

 all around the foot, and out upon the rostrum as far as the insertion of 

 the tentacles. Gills equal, symmetrical, their anterior third free, 

 and extending from a little behind the anal pore to the back of the 

 neck. Border of anal pore minutely serrate. 



In F. ( Cremides) barbadensis the edge of the mantle is not at all 

 fleshy, but is very narrow. It is not a simple edge, however, hav- 

 ing short papillose scallops on the upper and lower edges, as if 

 " pinked." 



Section Fissurella, s. str.. 



These typical Fissurella are confined in distribution to that 

 portion of the Western coast of South America washed by the cold 

 Peruvian Current, which is derived from the eastward moving stream 

 encircling the globe between 40 and 50 degrees S. lat. Upon strik- 

 ing the southern extension of S. America a portion of the current 

 is deflected downward around the Horn, the rest following the coast 

 up along Chili, leaving it in the neighborhood of Payta, Peru, 

 whence it turns toward the Galapagos Islands and becomes lost in 

 the Southern Equatorial current. The mollusks under considera- 

 tion therefore, probably do not find waters which become warmer 

 than about 70° Fahrenheit favorable to their existence ; in these 

 warmer regions they are replaced by other groups of Fissurella. 



The typical Fissurella, those having a distinct dark marginal border 

 inside, and with the edge of the shell not crenulated, fall into four 

 groups of species, thus : 



A. Hole long, its edges broadly eroded; interior wrinkled. 



Group of F. crassa. 



B. Edges of hole not much eroded ; interior not deeply wrinkled. 



a. Shell with radiating riblets. Group of F. picta. 



b. Shell ovate or elliptical, with radiating striae or smooth. 



Group of F. limbata. 



c. Shell oval or subcircidar, striate. Group of F. peruviana. 

 The last division (c, group of F. peruviana), contains species 



ranging from Peru northward to California ; thus falling outside the 

 limits imposed by physical conditions upon species of the other 

 divisions. 



