HABITS OF CARINAHIA. 521 



sented in a reversed position ; nor are snails that lead an 

 arboreal existence. The vertical expanded part of the 

 body of Carinaria and Atlanta is sometimes erroneously 

 regarded as a fin ; and in the figures of Rang, Blainville, 

 and De la Chiage, which are in an inverted position, this 

 idea would, in the eyes of the uninitiated, be confirmed. 

 Although I have myself frequently seen them swimming 

 in this reversed position after capture, they frequently 

 progress feebly with the shell uppermost. When fresh 

 and just taken, I have seen both the Carinarits and 

 Atlanta swim with their bodies in every position on their 

 sides, on their backs, and with the foot downwards. 

 The Carinarice are swift and rapid in their movements, 

 and dart forwards by a continuous effort, moving their 

 foot and caudal appendage from side to side, as a 

 powerful natatory organ, and do not progress by sud- 

 den jerks, like the Atlanta and Hyalaa. In these parti- 

 culars, my observations are conformable with the state- 

 ments of M. Rang. The true analogue of the foot of 

 Gasteropods in Atlanta and Carinaria is the sucking disc 

 placed at the posterior part of the vertically -flattened 

 appendage of the body, but its use is circumscribed to 

 that of enabling the animal to anchor itself temporarily 

 to floating bodies when fatigued, therein offering an 

 analogy to the gasteropodous genera of Notarclius and 

 Scyllaa, which cling, in the same manner, with the back 

 downwards, to floating sea-weed. The shell of the Cari- 

 naria, like that of the Testacella and Cryptostoma, covers 

 only a small portion of the body of the animal, defend- 

 ing the more delicate organs ; and in this we see a wise 

 provision for permitting these pelagic Mollusks to move 



