128 



(ECOLOGICAL NOTES. 



By Dr. A. E. Boycott, F.R.S. 



Read I2th November, 1920. 



1. POMATIAS ELEQANS ON SANDHILLS. 



There is a general agreement of record and experience that this 

 species is confined to calcareous soils, and its occurrence is often 

 sharply limited to small areas by the presence of chalk, etc., at the 

 surface. The probable explanation is that being largely subterranean 

 in habit and spending a good portion of its time underground it 

 requires a soil of a loose texture to burrow in. This is secured on 

 calcareous soils by the flocculating action of calcium carbonate on 

 the clay particles, which results in the dry granular loose surface 

 characteristic of such loci. In the south-west of England it occurs 

 on limestone near Ilfracombe (J. R. Tomlin, Jowrn. Conch., v. 1887, 

 p. 183), on chalk and greensand between Seaton and Sidmouth, where 

 the chalk reaches its western limit, and, I suppose on calcareous 

 greensand, at Torquay. Further west there are no calcareous soils, 

 but it is of much interest to note that it has been found in sandhills 

 on the coast at Perranporth (J. H. James in W. D. Roebuck's Census) 

 and Rock near Padstow (A. Gardiner, ib.) in Cornwall, and at Woola- 

 combe (M. J. LongstafE, Journ Conch., xiii, 1910, p. 23) in Devon. 

 At this latter place I have seen it pretty freely on the old sandhills, 

 now partly occupied by golf links, and in places dead shells are 

 abundant in the sand scraped out by rabbits in the rough pastures 

 to which the sand-blown coast has progressed at the southern end 

 of Woolacombe beach. This sandhill habitat is, I believe, quite 

 exceptional, perhaps because it is essentially mobile, unstable, and 

 often comparatively modern. It is obviously well suited for 

 burrowing. The facts suggest that the texture of the soil determines 

 the common preference of the species for calcareous places, but they 

 are by no means conclusive. For the sandhills are often, at any 

 rate, highly calcareous, as is shown by the massive deposits of 

 calcium carbonate which occur in their depths. The shore sand 

 itself contains the remnants of moUuscan shells, and where the dunes 

 are covered with vegetation the plants wijl collect lime from con- 

 siderable depths and bring it to the surface. This concentration of 

 lime in the upper layers may be assisted by Helicella virgata, which 

 eats the plants, and, living as it does for only one year (H. R. Bolton, 

 Naturalist, ii, 1852, p. 105), rapidly accumulates dead shells. 

 Helix aspersa, etc., have the same action. It remains, therefore, 

 uncertain whether the ordinary distribution of the species is 

 determined by chemical or physical considerations : one alternative 

 does not necessarily exclude the other. 

 [In discussion Mr. C. Oldham pointed out that Pomatias does 



