BOYCOTT : CECOLOGICAL NOTES. 169 



because it dries the surface of the ground and dryness is far more 

 destructive to the early stages than to the adults. In general, too, 

 it is probable that we should look to the causes of infant, rather than 

 adult, mortality for the agencies which keep snail populations 

 within bounds. 



Agriolimax agrestis seems to breed at any and every time of year ; 

 it lays eggs freely right through the winter in the milder spells. 

 Helicella itala, Cochlicella barhara, Vitrina pellucida, Hygromia fusca, 

 and Limax tenellus (of which the last three are certainly annuals) 

 are also late autumn or winter breeders. I do not know that any 

 of them occur on arable land, which is certainly about the last place 

 one would expect to find fusca (damp woods, etc.) or tenellus (ancient 

 woodlands.) 



[In the discussion on this paper the President, Mr. Grude, said 

 he had seen C. barhara on arable land in the Isle of Wight and 

 pointed out that winter breeding would be a protection for snails 

 living in the dry places (downs, sandhills, etc.), which are the 

 normal habitats of H. virgata, H. caperata, H. itala, and C. barhara. 

 Mr. Oldham reported H. itala on ploughed fields in Gloucester- 

 shire.] 



6. Balea pebvebsa and the GrEOPHOBic Habit. 



It is well recognized that the normal habitat of B. perversa is 

 " trees and walls ". The best summary perhaps is that of L. Reeve,^ 

 who says " crevices of walls, rocks, or trees ", for, as I believe, the 

 essential thing is that there should be narrow cracks and holes in 

 a dry place away from the ground. These are commonly afforded 

 by trees and walls, but the thatch of a barn will do.^ In Ireland 

 it occurs " on trees (sometimes fallen trees or logs), dry and mortared 

 walls and cliff faces " (A, W. Stelfox in litt.), and in the north of 

 Scotland, where it is common, it was never observed away from 

 walls.^ 



On trees it lives only on those which afford suitable shelter places 

 either by having a naturally loose rough bark (elm, apple, willow, 

 thorns on downs, ^ gorse bushes ^) or an adventitious coating of moss 

 or something equivalent. It is, for example, quite rare on ash and 

 oak^ or on normal beeches, but it may be found on the latter if 

 they are mossy or have loose bark owing to disease or have widely 

 open forks with a mass of dead leaves, etc. Round Aldenham it 

 occurs sparingly on many of the elms ( Ulmus cam'pestris), but I have 

 not found it on the oaks. On the elms it lives at the bottom of the 

 deep narrow cracks in the bark in places which are in summer dry : 



1 Land and freshwater Molluscs, 186.3, p. 106. 



2 In Oxfordshire ; W. Whitwell (Roebuck MS.). 



3 F. Booth, Scottish Nat., 1913, p. 253. 



* J. E. Harting, Rambles in search of Shells, 1875,"^. 89. 



^ J. R. Tomlin, Journ. Conch., xiii, 79. 



« In Glamorgan ; F. W. Wotton (Roebuck MS.). 



