302 CYCLOSTOMAT1D.E. 



at the base, as in Cochlicopa and Achatina. The epi- 

 phragm is extremely thin and glistening. The spire is 

 complete ; and in this respect it differs from that of the 

 shells belonging to species which British conchologisfcs 

 place in the genus Conovulus. The Rev. M. G. Berkeley 

 supposed that C. minimum might have the sexes distinct; 

 but the anatomical details of its structure given by Mo- 

 quin-Tandon prove that such is not the case, and that this 

 animal agrees in its mode of reproduction with all the 

 other members of the inoperculated Pulmonobranchs. 



The second section of the British Pulmonobranch 

 Mollusca comprises only the following 



Family V. CYCLOSTOMATID^E. 



BODY long and spirally coiled : mantle covering the front 

 or anterior part, and encircling the neck with an extremely 

 thin fold : snout strong and elongated : tentacles 2 only, con- 

 tractile : eyes at the external base of the tentacles : foot 

 long, distinct from the rest of the body. 



SHELL spiral, oval or cylindrical, and enveloping the whole 

 body : mouth round or oval : umbilicus small and narrow : 

 operculum paucispiral, testaceous or horny. 



This extremely numerous family has its home in the 

 tropics. Only two members of it inhabit this country ; 

 and each of these is included in a separate genus. As I 

 have before observed, many characters of organization 

 are common to the present family and the Pectinibranch 

 Mollusca. They are dioecious : their tentacles are two 

 in number and contractile : their eyes are placed at the 

 base of these tentacles : and their shells are furnished 

 with opercula. But their respiratory system is very 

 different, and corresponds with that of other families of 

 Pulmonobranch Mollusca. 



