168 PROCEEDINGS OF THE MALACOLOGICAL SOCIETY. 



are among the comparatively few places (apart from marshes, 

 moors, etc.) where one is unlikely to find maximum. Mr. Oldham, 

 whose experience with cwereoniger is exceptionally large, says 

 " my general impression is that you do not usually find the two 

 together, but this is not the invariable rule ", and gives details of 

 their concurrence in three beech woods in Bucks, Wilts, and Berks. 

 There seems, therefore, to be something in ancient woodlands which 

 maximus does not like ; we should perhaps regard it as the civilized 

 form of cinereoniger. 



5. Helicella vibgata and H. capebata in Ploughed Fields- 

 It is the experience of most collectors that land which is 

 actually in arable cultivation or has been under the plough in the 

 three or four preceding years is generally completely destitute of 

 land mollusca. Agriolimax agrestis is sometimes found and may 

 be abundant in seed grass, but the only conchifers which seem to be 

 able to survive the operations of agriculture are H. virgata and 

 H. caperata, including under the latter both cwperata seg. and 

 //. heripensis {^=gigaxii). The fact that these species are fairly 

 often found abundantly in the stubble of cornfields far from hedges 

 or uncultivated grass on calcareous soils has been commented on 

 by several observers,^ some of whom have particularly noted that 

 their abundance and size indicate that the conditions are favourable 

 and that they are not merely surviving with difficulty. These 

 observations correspond with my own experience, gained more 

 especially in Wilts, Hants, and Herts, and I would suggest that the 

 explanation of the exceptional habitats of these species is to be 

 found in their breeding habits. Both species lay eggs late in the 

 autumn (November-December), burrowing slightly into the surface 

 of the ground fco do so. I do not know when they hatch, but nothing 

 more is seen of them till about the following May, when quite young 

 individuals may be very abundant. After this they grow rapidly, 

 reach maturity, and die about Christmas, their whole cycle lasting 

 some twelve months. A certain number of caperata live through 

 the winter, and adults are not verj^ unoommon in the spring : virgata, 

 however, I have never seen alive and grown up at that time, though 

 a few probably survive sometimes. With normal cereal cultivation 

 this means that the eggs are laid after ploughing and sowing are 

 completed ; after this they are not disturbed for about nine months, 

 and when the upheaval of harvest and ploughing comes round 

 again they are two-thirds or three-quarters grown. If we assume 

 that the seriously vulnerable stages in the life history of snails are 

 the eggs and young, we have here an explanation of why virgata 

 can survive, while a species which lays eggs in the early summer 

 (e.g. Helix nemoralis) is obliterated : arable cultivation is detrimental 



1 S. S. Pearce, Journ. Conch., vi, 123 ; C. Ashford, ib., v, 162 : J. McMurtrie, 

 ib„ vi, 4 ; L. E. Adams, ib., ciii, 318 ; J. W. Horaley, ib., x, 48. 



