29 



HELICID^. 



The snails are provided with spiral, often turreted, rarely 

 depressed, or expanded shells, which, however, is never 

 operculated. In the deficiency of operculum the animal, 

 when hyhernating, closes the orifice with a membranous 

 epiphragm, perforated for the admission of air. The head 

 is well developed and furnished with retractile tentacula, 

 the two upper ones always prominent and bearing the 

 eyes at their extremities. These tentacles are always 

 cylindrical. 



The British ffelicida and other tribes of our testaceous 

 pulmonifera have formed the subjects of so many essays 

 and monographs that we do not deem it necessary to 

 treat of them at the same length, or to enter into details 

 of their habits to the same extent that we have done 

 in our account of marine mollusca, in order to keep our 

 work within proposed limits, already considerably ex- 

 ceeded. 



VITRINA. Draparnaud. 



Shell thin, translucent, oblong or suborbicular, of few 

 whorls, the last ample, the spire depressed ; aperture 

 rounded or oblong, large, lunate, entire ; peristome thin ; 

 columella imperforate. 



Animal bulky, large for the shell, lanceolate ; head 

 with four tentacula, the lower pair short ; mantle ample, 



