228 BERMUDA. 



We know of only one genus representing this 

 order, viz. the Tritonia. The Mollusca which form 

 this genus have the body oval-oblong. The species 

 observed here is the Tritonia arborescens. 



III. Gasteropoda InferoHranchiata. — These have 

 nearly the habit and organization of the preceding 

 order; but their branchias, instead of being placed 

 on tjie back, resemble one or two long series of 

 laminae under the mantle, either surrounding the 

 body, or on the right side only. The species are 

 strictly littoral, being gasteropodous, and incapable 

 of swimming. 



Genus Ancylus represents this order ; the species 

 is the Ancylus rivularis. It is found adhering to 

 stones and aquatic plants in ponds. 



IV. Gasteropoda Bectibranchiata. — These have 

 their branchise on the back, a little inclining to 

 the right, composed of laminae more or less divided, 

 but not symmetrical, generally protected by expan- 

 sions of the mantle, in ^hich there is usually a 

 small shell. 



They are hermaphrodites, like the Nudibranchiata 

 and Pulmonea ; and resemble the Pectinibranchiata 

 in the form of the respiratory organs, and, hke them, 

 live in the sea. 



The genus belonging to this order is the Bullcea. 



