142 CARDIAD^. 



most conspicuous along the posterior slope, where they are some- 

 times folded so as to assume the form of spines ; interior white or 

 flesh-colored, sometimes with a brownish blotch at the 



Fig. 452. . 



posterior muscular impression ; furrowed to correspond 

 to the ribs without. Length, nine twentieths of an inch ; 

 height, f(un- tenths of an inch ; breadth, three tenths of 

 an inch. 



C. piimiilatitm. . n i • • 



ilns very small and pretty species is as common as 

 any other shell in the stomachs of fishes, and may be obtained from 

 them at almost any time. Mr. Conrad obtained his specimens from 

 Massachusetts, and I have never heard of it in any other locality. 



Charles River, three to seven fathoms, gravelly l)ottom (^Sf imp- 

 son} ; Eastport, pretty common ( Cooper} ; Halifax and Fishing- 

 Banks (^Willis}; Casco Bay (Mi^rhels') ; Gardiner's Bay, Long 

 Island {S. Smith). 



It is usually accompanied by the young of C. Islaudicum, from 

 which it is distinguished hy fewer ribs, and the scales crossing 

 them. It is at first difficult to say that it is not identical with one 

 of the small European species, which are scarcely distinguishaljle 

 from each other by mere size and form, but require a careful ex- 

 amination of the sculpture in order to separate them. From C. 

 exiguum it differs in not having a short, diminished anterior side, 

 elevated beaks, and a very prominent ridge posteriorly, and especially 

 in the absence of pits in the grooves. The whole aspect of that shell 

 is angular, while our shell is scarcely at all so. It is still nearer to 

 C. fasciatum and C. nodosum^ agreeing most with the former in out- 

 line, and with the latter in sculpture. C. fasciatum., however, has 

 mere points and not bars along the posterior ribs ; and while the 

 sculpture is almost precisely the same as that of C. nodosum^ it is 

 more broadly rounded anteriorly and less angular posteriorly, with 

 a less strongly marked oblique ridge, so that on the whole it has a 

 more rounded and lenticular form. In the young shell all the ribs 

 are traversed by the transverse bars ; but by age those on the disk 

 become worn off, and they are only found on a few ribs at each 

 end. The animal sometimes suspends itself by a thread, and can 

 leap by its foot to a considerable distance. 



Ocniis LIOCARDIUM, Morch. 



Shell longitudinally oval, inequilateral ; surface of valves simple, 

 neither ribbed nor spinous ; hinder gape small. 



