PEARCE : VARIETIES OF BANDED SNAILS. I25 



oi Helix caperata, and also those oi Helix virgata are tound on 

 arable ground, especially in the borders of culitvated fields in 

 limestone districts, size would seem to depend only on the 

 combined presence both of an abundance of food-plants such 

 as are supplied in the cultivated field, with a calcareous soil. 

 Proper herbage apart from the calcareous earth, and vice versa, 

 the calcareous soil without the richer food-plants will not suffice 

 to increase the shells in size. The two conditions must be 

 united and then a consequent largeness seems to result, at any 

 rate the largest individuals of both Helix capeixtta and of Helix 

 virgata in my collection came from the borders of cultivated 

 fields on a chalk soil, in the county of Sussex ; while on the 

 open down close by, in the sand neighbourhood where there is 

 an absence of the richer herbage found in the tilled field*^, 

 though the chalk formation may be identically the same, only 

 shells of the usual or smaller size can be gathered. 



In the next place, with regard to that more important 

 Variation in Form or Shape, Helix caperata exhibits only t^co 

 lines of divergence, either we find that the shell is a compact and 

 close one with a somewhat raised spire — (we have an extreme 

 embodiment of this variation in the var. subscalaris of Jeffreys' 

 in B.C. Vol. I. p 214), — or else, instead of the compact shell, 

 we have a looser shell with a flattened spire and a wider 

 umbilicus like to Jeffreys' var. 4 Gigaxii. 



It is to be noticed that whilst we find the latter of these 

 two distinct forms in the borders of fields, and especially in 

 clover fields, the other more compact variety seems to keep 

 entirely to the open downs and pastures and uncultivated places, 

 like sand-hills, etc., where it is so frequently associated with 

 Helix virgata. Perhaps it is in these different habitats that we 

 discover the explanation of how these two distinct forms of 

 Helix caperata have come into existence. In the tilled fields 

 where we always find the variety with the less compact shell 

 like the var. Gigaxii, the flatter shell is of more use, enabling 

 the snail the better to crawl about with house low down upon 



