291 



TWO MOLLUSCAN ASSOCIATIONS IN 

 NORTH-EAST STAFFS. 



By W. E. ALKINS, M.Sc. 



(Read before the Society, November 12th, 1919). 



A COMMITTEE of four was appointed in 1900 by the Council of this 

 Society " to consider and, as far as practicable, to carry out collective 

 investigation into the phenomena connected with the variation and life- 

 history of land and freshwater mollusca" (y. of C, vol. 10, p. 32). 

 Two lists, each containing five subjects for enquiry, were published 

 (/.<:., pp. 28 and 88), but unfortunately the committee did not receive 

 "sufficient information on which to base a report," and did not seek 

 reappointment for a tliird year (i.e., p. 276). 



Two of the selected subjects on the second list read : — " ii. Do 

 Tachea nemoralis and T, hortensis occur together or separately? 

 (i) in the same district, (2) in the same locality, (3) in the same kind 

 of habitat?" "iii. Do Clausilia nigosa (bideyitata) and B a lea per- 

 versa occur together? What habitats are they usually found in?" 

 The former association forms the subject of two short papers which 

 appeared later in the same volume (p. 300 : S. S. Pearce : The 

 Association of Helix nemoralis and Helix hortensis; p. 302: R. 

 Welch : The Association of Helix fiemoralis and Helix hortensis in 

 Ireland) ; while the latter is dealt with by R. Welch a few pages 

 further on (p. 312 : Clausilia bidentata and Balea perversa in Ireland). 

 I. H. nemoralis and H. hortensis. 



The Rev. S. S. Pearce had only taken H. nemoralis and H. 

 hortensis in association in five localities ; it is, perhaps, significant 

 that three at least of the five are situated in chalk or limestone 

 districts. 



He concludes that " as a rule the two species live in separate and 

 distinct , . . habitats." On the continent he had taken both 

 species in France and in Switzerland, in each case without associa- 

 tion ; the suggestion is made that in the Alps H. hortensis generally 

 ranges higher than its ally — though why this fact should preclude 

 association below the limit reached by H nemoralis is, perhaps, not 

 very clear. 



Mr. Welch remarks on the general rarity of H. hortensis in Ireland. 

 He had taken it in four localities : — 



1. On quartzites at Portsalon, N.W. Donegal; H. nemoralis 

 not taken. 



2. From Ordovician rocks, capped with boulder clay, at Down- 

 patrick, Co. Down ; H hortensis very rare outside, but predominating 

 inside, the cathedral graveyard. 



