ltfU9-J.9.LU.J -jqq 



interest of the paper. Mr. Tomlinson also exhibited a fine 

 collection of hand specimens of the rocks and fossils of the 

 district. 



"variation due to environment, illustrated mainly 

 by the mollusca." 



At a meeting of the Zoological Section on 2nd March, Mr. 

 R. Welch, M.R.I. A., read a paper on the above subject. Mr. 

 Welch, in introducing this subject for discussion, first referred 

 to the special succeptibility of plants to variation due to their 

 environment, giving examples of very marked cases due to differ- 

 ences in soil. He exhibited specimens of Pyrola, Sysimbrium, 

 Orchis, etc., from Mr. N. Carrothers' herbarium. Passing to the 

 Mollusca he mentioned instances of restricted areas where white- 

 shelled forms of species usually found with dark shells are common. 

 Altitude seems at times to affect the size and colour of shells very 

 much, and cases were mentioned and specimens exhibited to 

 illustrate these points. The question of variation in size, texture, 

 and shape of certain fresh-water species living in varying volumes 

 of water such as large and small lakes, ponds, and drains, also 

 the effects of life in running and in still water were discussed. 

 Examples were shown of Li/nncea stagnalis and Anodonta cygnea 

 including the very large form — 9 inches in length— from a small 

 pond near Preston. 



The speaker next referred to the generally smaller sizes of 

 shells on islands as compared with those on the mainland, but 

 mentioned some marked exceptions, such as the very large Helix 

 nemoralis from the Aran Islands and Inishmurry on the West 

 Coast of Ireland. The large proportion of white-lipped forms of 

 the last species that live on the north-west Donegal Coast, and the 

 heavy forms that occur on bare areas of the sand-hills where 

 the only plant is Psamma arenaria with an occasional Senecio 

 Jacobcea, were spoken of and specimens exhibited. 



