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ON THE ASSOCIATION AND NON-ASSOCIATION OF HELIX 

 NEMORALIS Linne AND HELIX HORTENSIS Miiller. 



Hy W. CARTWRIGIIT, O.B.E., M.Sc. 

 (Rend Ifefore the Society, May 6th, 1922). 



Introduction. 

 In a recent paper to the Conchological Society ^V^ E. Alkins gave 

 an account of the association and non-association of Helix nemoralis 

 Linne and Helix hortensis Miiller in N.E. Staffordshire ; in con- 

 clusion the author appealed for more data and it is with the object of 

 placing on record some further material that the present paper has 

 been written. At the present time we do not know to what cause or 

 causes the distribution of the various speci*es is due, and H. horteftsis 

 and H. nemoralis have been selected because they are found associated 

 and in separate colonies in stations which, at first glance, appear to 

 possess the same essential features. It is hoped, therefore, that a 

 detailed study of the habitats of these two species in the Buxton 

 district of Derbyshire will bring to light some facts that will serve to 

 elucidate the problem of their association and non-association. 



All the stations which are discussed in the following pages are 

 situated on the Carboniferous Limestone, which is exposed in a broad 

 anticline, the axis of which passes between Buxton and Millers Dale. 



Millers Dale. 



A considerable colony of H. nemoialis and H. hortensis occurs on 

 the bank lying in the angle formed by the Litton and the lower 

 Tideswell roads and another, though smaller colony, is found on the 

 roadside just above the Tideswell road. 



The habitat of the former colony consists of a steep bank with a 

 south aspect covered to within a few yards of the bottom with long 

 coarse grass which then gives place to a much shorter and finer 

 variety. The upper portion of the bank is more damp than the few 

 yards immediately above the Litton road, a circumstance due in a 

 large degree to the fact that the drainage from the Tideswell road flows 

 on to the top of the bank. Along the upper portion of the bank 

 mud, washed from the road above, has accumulated below the 

 drainage holes, forming mounds which extend for some yards down 

 the hillside ; these mounds are always covered with a bed of nettles 

 {Urtica, sp.) with occasionally brambles {Rubus, spp.) and wild sage 

 {Salvia, sp.). Along the lower and drier portion of the station, the 

 underlying limestone frequently crops out. 



External conditions have thus divided this habitat into two more 

 or less distinct parts and this reflects on the distribution of the 

 molluscs. It cannot be said that H. nemoralis and H. hortensis are 



