PEARCE : ASSOCIATION OF HELIX NEMORALIS AND H. HORTENSIS. 30I 



)redominates over the other species in the Tor Bay district, the 

 lumbers taken being H. Jiemoralis 136, H. hortensis 34. 



The foreioins then are the occasions when I have myself during 

 I considerable number of years noticed the actual association of the two 

 ;pecies. The cases of association appear to be so rare, or at any rate 

 lave been so infrequently recorded by others, that we may safely 

 conclude that as a rule the two species live in separate and distinct, 

 hough not always (and this is the puzzle to my mind) in different 

 vinds of habitats. As far as our own country is concerned it is difficult 

 suggest any explanation as to the tendency of these snails to inhabit 

 ;eparate localities with only occasional overlapping. 



Turning to the continent, I have observed one or other or both of 

 he species in many places, in P>ance (N.W., W. and S.E.) without 

 issociation; in Switzerland (VV. and Central) without association; and 

 n Italy (N.) where I have only taken Helix fiemoralis. H. hortensis is, 

 [ believe, recorded from the north of Italy, but it seems to me that 

 he white lipped variety of H. nemoralis, which is not uncommon in 

 Lombardy, has perhaps been mistaken for JI. hortensis. 



In the vicinity of the Alps, however, I think there are facts which 

 ;o my mind tend to demonstrate that, among other circumstances, 

 ;hat of altitude has a voice in determining the range of the two species. 

 For instance while staying near Geneva in 1895 on the Grande Saleve 

 aiountain, which rises to some 4,600 feet, I found H. hortensis 

 abundantly on loose stone walls and under heaps of stones at a level 

 of 3,500 feet and upwards in company with H. arbustonim, H. 

 sylvaiica, H. lapicida and other smaller forms. H. nemoralis on the 

 other hand does not reach higher than 2,340 feet, at the height of the 

 village of Monne'tier where I took a few examples. Thence down- 

 wards it increased in abundance, abounding on every tree, wall and 

 hedge between 2,000 feet (about) and the level of the Lake of 

 Geneva. 



Apparently the same tendency of H. hortensis to reach higher parts 

 than H. nemoralis is observable in Central Switzerland; at Berne, H. 

 nemoralis is plentiful, but at Thun (1,850 feet, about 150 feet above 

 Berne) H. hortensis appears only, as far as I know, and proceeding 

 up the valley from Thun to Interlaken (1,857 feet) past Brienz (r,857 

 feet) on to Meiringen (1,970 feet) and up the Brunig Pass (3,396 feet) 

 H. hortensis is found exclusively, though not abundantly. Perchance 

 some of your correspondents may be able to give some precise 

 information as to the distribution of H. hortensis in the Alps. 



The Rev. J. \V. Horsley in this Journal (vol. 7, p. 34) gives an 

 interesting instance of the intrusion of Helix nemoralis into the valley 

 of jMeiringen. 



