PELECYPODS 



455 



and C. quadrigenarium on the southern shores of California. The former 

 is a full, round, heart-shaped shell with about thirty somewhat scaly 

 ribs. The edge of the shell is deeply toothed ; the color light brown- 

 ish ; the diameter from two to three inches. It preserves all the features 

 of the genus as regards both shell and anatomical characters. The other 

 species, C. quadrigenarium, very strongly resembles C. magnum in size 

 and shape. It lacks 

 the flattened area on 

 the posterior portion 

 of the shell which is 

 characteristic of the 

 east-coast species, and 

 its uniform brownish - 

 white coloration is less 

 striking. It has about 

 forty regularly spaced, 

 radiating ribs, which 

 are smooth upon the 

 umbonal region, but 

 elsewhere are armed 

 with spiny processes. 

 Diameter about six in- 

 ches.(PlateLXXXIV.) 

 C. islandicum, C. 

 pinnulatum. Both 

 of these are cold-water 

 species and occur along 

 the New England coast. 

 The former has a shell 

 which varies from one half of an inch to two inches in length, and has from 

 thirty-six to thirty-eight sharp, three-sided, radiating ribs, the furrows 

 between them being rounded and wrinkled by growth-lines. A yellow- 

 ish-brown epidermis covers the shell and bristles into a sort of fringe upon 

 the sharp edges of the ribs. C. islandicum cannot be said to be a very 

 common species in New England, although coUectors have so reported it. 

 Specimens from Massachusetts are not as large as those of more northern 

 habitat. It does not occur south of Cape Cod. C. pinnulatum is one of the 

 "small fry" among the cockles. Its largest diameter is less than one 

 half of an inch ; but what it lacks in size it seems to endeavor to make 

 up in abundance, for it is scattered everywhere along the 

 coast from New York northward. Specimens can nearly 

 always be found in the stomachs of fishes, which, by the way, 

 form an excellent hunting-ground for rare species of mol- 

 lusks of small size. There are twenty-six slightly rounded 

 ribs, with deep linear grooves between them. Upon the ribs, 

 especially in the posterior portion of the shell, are arched 

 scales, folded so as to appear like blunt spines. The species 

 may easily be distinguished from the young of C. islandicum by the 

 smaller number of ribs. The animal, C. pinnulatum, is said to be exceed- 

 ingly lively and able to make rapid progress over gravelly bottom by exe- 

 cuting sudden leaps. It has a long, recurved, very strong foot, and its 

 movements are effected as described above. It is abundant at Bar Harbor. 



Cardium islandicum. 



