109 



Tarn. 2. HELICID^. 



Head and tentacles retractile, like the former, but 



the end of the tail is tapering, and destitute of any 



gland. The pulmonary cavity is generally in 



the front of the body ; the respiratory hole is on 



the hinder part of its edge ; and the orifice of 



the generative organs is placed near the hinder 



outer base of the right tentacle. 



This family contains more than half of the British 



land and fresh- water shells, that is, 72 out of 128 



species. It has been divided into several genera, and 



there are many more exotic ones. They have been 



distributed into sections in the following manner. 



I. Body elongate, attached by its whole length to the 

 foot ; mantle shield-like. 



* Mantle shield-like, simple, entirely enclosing the 

 shell. (Limacina.) 



1. Umax. (p. 103. f. 2.) 



* * Mantle shield-like, icith a partly external, thin, 

 central, spiral shell. (Vitrinina.) 



2. Vitrina. (p. 103. f. 3.) 



II. Body spiral; mantle thin with a thickened edge, 

 lining the inside of an external shell. 



* Body with tivo longitudinal grooves ; lips cylindrical, 



retractile. ( Testacellina. ) 



