180 



CYPEINID.E. 



ill contact ; anterior part shorter, narrower, rounded and com- 

 })ressed ; posterior part full and l)i-oad at the hack, slightly angular 

 at the extremity ; a very superlicial ridge passes from the heaks to 

 the lowest posterior point ; the space which they include is very 

 coarsely wrinkled ; there is a shallow oval pit hefore the heaks, hut 

 no distinctly marked lunule ; the ligament is strong and protuber- 

 ant ; epidermis of a dark, shining, burnt-brown color, sometimes 

 almost black, coarse and strong, rough with crowded and loose 



C. Islandica. 



wrinkles ; hinge-margin broad and strong ; cardinal teeth diverging, 

 tln-eo in each valve, or rather one large doulde tooth and a small 

 one in the right valve ; marginal tooth slightly developed, blunt ; in- 

 side chalky-white, muscular and pallial impressions superficial, the 

 latter having no sinus ; margin at base sharp and simple. Length, 

 ihree and a half inches ; height, three inches; breadth, one and 

 three fourths of an inch. 



This shell is an inhabitant of all the Northern Atlantic seas, es- 

 jiecially near where some river empties into the ocean. It is some- 

 times thrown up from deep water upon our beaches in great num- 

 bers after storms. The young are found abundantly in the stomachs 

 of fishes taken in Massachusetts Bay. It appears not to be com- 

 mon, if it is found at all, to the southward of Massachusetts. 



