CHAPTEE Y. 



A Ramble over the Chalk The Edible Snail Its supposed Intro- 

 duction Culture of Edible Snails The Heath, Zoned and 

 Wrinkled Snails The Rock Snail Its supposed power of boring 

 The Kentish Snail and other local species. 



So far as we are aware, there are no aquatic 

 mollusca, either bivalves or univalves, peculiar to 

 the chalk, and almost all that have been mentioned, 

 as inhabiting the London clay, are equally at home 

 on the lighter and whiter soil. But amongst the 

 terrestrial univalves there are several which are 

 only to be found upon chalky ground, and must 

 therefore be sought at a distance from the metro- 

 polis. The greater number of these belong to the 

 true snails (Helix), most of which are well marked 

 and easily recognizable species. 



With regard to the largest of them, the edible 

 snail, Helix pomatia (PI. IX., fig. 4), there 

 appears to be some doubt whether it is an in- 

 digenous or imported species in this country. 

 Some have supposed it to have been introduced 

 by the Komans ; but there seems to be no other 

 foundation for this idea than that it is found in the 



