164 PROCEEDINGS OF THE MALACOLOGICAL SOCIETY, 



Bithinia leachii, etc., which extend through the greater part of 

 England, or (b) like Helix pomatia, Theba cartusiana, Helicodonta 

 ohvoluta, Ena montana, Clausilia hiplicata, which have a much more 

 restricted range. 



The contrast between the north-western and south-eastern 

 groups appears quite definite. It has presumably in part arisen, 

 like the similar distribution of human culture, from the geographical 

 position of England in relation to the Continent, but it is at least 

 possible that the prevailing meteorological conditions have some- 

 thing to do with it in both instances. Maps are shown (PI. V) 

 giving the data as regards temperature and rainfall in a summary 

 fashion. It would be a long matter to discuss the best form in which 

 these factors should be considered. Rainfallis no doubt more impor- 

 tant qua snails at one time of year than another, whether it falls in a 

 few large or many small doses is no doubt germane, the proportion 

 of rainy days and their seasonal distribution require notice. The 

 humidity of the air would be of the greatest interest if there were 

 any data available worth consideration. Similarly the seasonal 

 and diurnal temperatures and their ranges will ultimately require 

 analysis, the night temperature being perhaps more interesting to 

 nocturnal animals like slugs than to ourselves: the "accumulated 

 temperatures " above some fixed point divised by Strachey for 

 agricultural purposes suggest an interesting line of inquiry. Local 

 differences within the same area may be considerable, the relation 

 of rainfall to altitude being the most conspicuous. Viewed, however, 

 in a broad way, no one can doubt that the crude maps of total 

 rainfall and mean temperatures for January and July (PI. V) show 

 plainly that the south-east has a very different climate to the 

 north-west : in brief summary, the south-east is as cold or colder 

 in winter, hotter in summer, drier and more sunny. 



It is instructive to compare with the snail distributions two 

 maps showing the proportion of the acreage of what the Board of 

 Agriculture calls " cereal crops " (wheat, barley, oats, rye, beans, peas) 

 occupied in each county by wheat and oats respectively (PI. V). 

 In the former the country is shown in four areas, in which wheat 

 occupies 15 per cent and under (plain) of the cereal land, 16 to 25 per 

 cent (sparsely dotted), 26 to 35 per cent (thickly dotted), and more 

 than 35 per cent (black) : in the latter the groups are under 25 per 

 cent (plain), 25 to 49 per cent (sparsely dotted), 50 to 74 per cent 

 (thickly dotted), and 75 per cent and over (black). Here again the 

 exact form of comparison is open to considerable discussion and 

 elaboration ; the main conclusions, however, come out m.uch the same 

 whatever method is adopted. In a general way the distribution of 

 wheat and oats may be taken to be determined by climate ; a farmer 

 will always grow wheat in preference to oats if he can, and the 

 influence of soil has been largely obliterated by modern methods of 

 cultivation and manuring : wheat is concentrated and valuable, so 



