CONCHOLOGY. 107 



Species more or less depressed, umbilicated, Planorbis- 

 shaped, the edges of the aperture thickened, callous, and 

 even toothed. 



H. conoides. The cone-shaped Snail. PI. 18, fig. 4. 

 Species conoidal ; the turns of the spire rounded. 



H. pomatia. The edible Snail. 



Species sub-globular, not umbilicated ; the margin of the 

 aperture thickened ; aperture covered with a calcareous lid 

 resembling an operculum. 



H. nitida. The pellucid Snail. 



Species depressed, more or less largely umbilicated ; the 

 edges sharp, but always thin and shining. 



H. nemoralis. The grove Snail. 



Species imperforated, semi-globular, thin, and sub-pel- 

 lucid ; not umbilicated, with a light inflexion at the place of 

 the junction of the columella with the margin of the aper- 



