333 INTEODUCTION TO COXCHOLOGY. 



strong power of attacliment, allows of a more simple con- 

 dition of the hinge; the teeth are consequently smaller, 

 and the ligament weaker. 



Here, then, is another, and very obvious instance of adap- 

 tation to existing circumstances. Area of the first division, 

 which are free to range according to their inclinations, 

 possess solid and ponderous shells : they have frequently 

 to encounter storms and rolling seas, and are consequently 

 liable to be tossed on rocky shores. Those of the second 

 division, which can safely moor themselves to the rocks, 

 remain undisturbed amid all the fury of the contending 

 elements. 



An interesting monograph of the Area family has been 

 published by Mr. Lovell Reeve. It includes a considerable 

 number of new species, with distinct descriptions of each. 



The dwelling-place of very many among its members is 

 in sand or mud, at considerable depth. The Beautiful Ark 

 {A.formosa) was found in the Gulf of Tehuantepec, Mexico, 

 calmly reposing beneath the waters ; it was invested with 

 an epidermis, of wliicli the bristles were at least half an 

 inch long at the end of the shell. The Copperas Ark 

 [A. chalcanthum) appears as if stained with green copperas ; 

 it was first discovered by Mr. Cuming, in sandy mud at 



