48 



THE ZOOLOGIST. 



and opaque white as regards the ground colour, at about 500 ft. 

 or 600 ft. or so, is not much more than half the diameter and semi- 

 diaphanous at 900 ft. to 1000 ft. above the sea-level. To a less 

 degree also H. caperata is similarly affected concerning colour, 

 but altitude appears not to influence it in size, for large speci- 

 mens may be found at all the higher elevations. H. virgata is 

 of comparatively larger size — at least, many individuals attain 

 to such — at the lower levels, especially on the lias clay at from 

 200 ft. to 300 ft., the average becoming smaller the higher the 

 species is found. Although it has a wide area of distribution in 

 the Cotteswolds, it is rarely found in such prodigious abundance 

 as is the case on the chalk downs further south. In the Cottes- 

 wolds it seems to abound principally on the higher parts of the 

 pseudo-plateau and hill tops, often in the most exposed places, 

 while few or none at all are to be found below. This, I assume, 

 is owing to the absence of organic competition in the shape of 

 animal enemies at the higher altitudes, otherwise, no doubt but 

 for their presence it would be at least equally plentiful in many 

 lower localities than is the case, and where the climate would be 

 more congenial to its taste. It seems to be the most hardy 

 species of mollusc which we possess, judging from the absence of 

 shelter in the situations it frequents, and at altitudes where the 

 greatest vicissitudes of temperature prevail. 



In the case of arboreal species, the presence or absence of 

 shelter afforded by the beech woods appears to have more effect 

 in fixing the morphology than absolute altitude above the sea- 

 level ; for many species are much larger and of deeper coloration, 

 or else of a more pellucid character in the former environment, 

 than they are even at lower elevations without. Special men- 

 tion may be made in this connection of Helix nemoralis, H. hor- 

 tensis, Helicigona arbustorum, H. lapicida, Clausilia bidentata, 

 and Jaminia secale, among others, while with regard to those 

 which dwell principally in moss and rarely expose themselves to 

 the air, such as Vitrea crystallina, I have not observed any 

 apparent diminution in size even at the highest altitudes. 



The great majority of the species of Cotteswold Terrestrial 

 Mollusca range up to fully 950 ft. above the sea-level — that is, to 

 the extreme upper limits of the arborescent vegetation. All the 

 slugs are thus found, I believe, with the exception of Testacella 



