CHAPTER x 



PHYLUM X.: MOLLUSCA (continued) 



AIR-BREATHING LAND SNAILS 



LAND Snails are characterised by possessing two pairs of 

 hollow tentacles, the eyes being placed at the tip of the 

 hinder longer pair. 



The shell may be well developed and spirally coiled, or it 

 may be absent, or represented by a few calcareous particles 

 only, as in many slugs. 



No land snail has a true operculum, and all are herma- 

 phrodite. 



Type : The Common Garden Snail (Helix aspersa). 



One striking point of difference between the shell of a 

 land snail and that of a pond snnil is the greater thickness 

 and strength of the former. The thickness of the shell 

 seems to vary with the nature of the soil, and the consequent 

 character of the plants on which the snail feeds. 



In Helix aspersa the shell is fairly thick, and 

 is spirally coiled, but the spire lies quite to the 

 right of the body whorl, and is much blunter than in Limnaaa 

 stagnalis. 



The colour of the shell is yellowish, with spiral dark 

 reddish-brown bands running round it. There may be as 

 many as five of these bands on the body whorl, but frequently 

 some are confluent. The bands are always interrupted, more 

 or less, by transverse irregular streaks of white or yellow. 

 The white lip of the shell is thickened, and turned outwards. 



126 



