274 HELICID^. 



Up nearly straight : umhilicus forming a narrow and oblique 

 slit. L. 0-275. B. 0-1. 



Var. viridula. Shell greenish-white and transparent. 



Habitat : On the trunks of trees (chiefly of beech, 

 ash, sycamore, and apple), as well as on mossy rocks 

 and walls, in various parts of Great Britain and Ireland 

 from the Moray Firth district to Guernsey. The variety 

 was found near Cork by Mr. Humphreys. Professor 

 Morris has noticed this species as fossil in the upper 

 tertiary deposit at Grays. It ranges from Finland to 

 Sicily, and even to Madeira and the Azores. It is widely 

 diffused in Europe. 



The Tree-snails are gregarious, and are found of differ- 

 ent ages in the same spot, as if forming a sociable family 

 party. It is difficult to discover them in dry weather, 

 as they lie concealed in crevices of rocks or under the 

 bark of trees ; but after rain they come out from their 

 hiding-places and feed on the moistened vegetation. 

 They are not particularly sensitive, and do not withdraw 

 into their shells on being touched or disturbed ; nor 

 are they afraid of cold, having been observed crawling 

 about when the temperature was very little above zero. 

 Puton found specimens on the Vosges Mountains at a 

 height of nearly 2300 feet. Bouchard-Chantereaux says 

 that B. perversa lays, in the beginning of autumn, from 

 12 to 15 whitish and globular eggs, which are of a large 

 size compared with those of most other snails, and that 

 the young are excluded or hatched on the fifteenth or six- 

 teenth day afterwards and become adult at the end of 

 their first year. Lister stated that the sexes were distinct 

 in this species, and that there was a difference of size 

 between the male and female, the latter being more 

 bulky; but Dr. Gray very properly remarks that this 



