OF CONCHOLOGY. 85 



thina, Helix, Lymnea, BuHmus, Mela- 

 nia, and Planorbis. 



In Turton's Linne 267 species of 

 Helix are described ; and 67 species 

 have been ascertained as indigenous 

 to Britain, 



Genus 30tb.— NERITA. Animal 

 a Limax; shell univalve, spiral, gib- 

 bous, flattish at bottom ; aperture 

 semiorbicular, or semilunar; pillar-lip 

 transversely truncate, flattisb. Linn. 

 Syst. 329 Plate 9th, fig. 30tb. 



This genus is divided into three 

 families : *Umbilicata?, umbilicate ; 

 **lmperforat8e, &c. imperforate, with 

 the lips toothless ; ***Imperforate, 

 with the lips toothed. 



Habitation. The Nerita? inhabit 

 the sea, lakes, and rivers. Those in- 

 habiting the sea are, for the most part, 

 found near the shore, and several are 

 attached to marine plants ; and some 

 are only found in deep water, so that 



