171 



careous operculum, protecting them from injury or in- 

 trusion, while they remain in an inactive or torpid state: 

 and such is their tenacity of life, that the writer has 

 received shells of this genus from the Brazils and the 

 West Indies, closely packed in boxes, which, shortly af- 

 ter they were opened in this country, exhibited these 

 animals gladly escaping from their confinement, appa- 

 rently uninjured by the length of their journey, or the 

 want of air and sustenance — It is also a well attested 

 fact, that a portion or even the whole of this animal's 

 head will be reproduced, after having been severed 

 from the body, by accident or cruelty. 



Shells thus clearly characterized cannot easily be 

 mistaken, and may reasonably be supposed to form the 

 testaceous covering of molluscous animals, all of which 

 have a similar organization of parts — A fact assumed 

 by Lamarck, as the basis of his systematic arrange- 

 ment, and satisfactorily established by a host of evi- 

 dence, either derived from the examination of the ani- 

 mal while living, or where that was not practicable, 

 from a constant and uniform concurring similarity of 

 structure in the shell. In this genus the naturalist may 

 easily witness the process of the animal's forming its 

 shelly dwelling upon the model of its naked body, com- 



