CHASTER : A CROSS BETWEEN L. STAGNALIS AND L. AURICULARIA. 283 



nalis, L. auricular ia, and L. peregra are to be considered as distinct 

 forms, or as mere races or sub-species of a single species. Most 

 conchologists, I doubt not, would positively pronounce them dis- 

 tinct, though some — and those attentive and experienced students of 

 the group — -would express a doubt. I do not propose to enter into 

 a long discussion upon the value of various morphological differences 

 as data for separating species, but will merely emphasize the fact that 

 no differences, conchological or malacological, are sufficient to sepa- 

 rate two forms as distinct species unless a sufficient number of 

 observations have been made to prove that these differences are 

 constant and that intermediate forms do not occur to bridge over the 

 distinctions. In the case of land and fluviatile Mollusca, with their 

 extremely variable environment, we should expect to find great varia- 

 tion occurring — variation becoming more and more pronounced and 

 permanent until at last races or sub species are produced which no 

 longer revert back to the primitive form when they are re-introduced 

 to earlier conditions of life. (Such races are easily exemplified in 

 Homo sapiens). Too often, unfortunately, does the conchologist 

 ignore the scientific aspects of this difficult problem ; too often does 

 he hasten to describe as a 'new species' a specimen presenting some 

 trivial difference from others occurring in neighbouring localities ! 

 Quite recently I noticed six 'new' species of Succinea described from 

 the Sandwich Islands alone, some of them apparently based on char- 

 acters such as specimens from different British localities often present 

 in the case of our S. putris. 



The remarkable progeny of the Limncza just described appears to 

 afford ph)logenetic evidence of considerable importance. Everyone 

 is of course familiar with Charles Darwin's classical observations on 

 the reversion of the offspring of crossed breeds of pigeons to the 

 primitive stock. Have we not here a quite analogous case? May we 

 not justly conclude that L.peregra represents the primitive form from 

 which have arisen L. stagnalis and L. auricularia, whether these are 

 looked upon as races or as species ? It seems difficult to escape 

 from such a line of reasoning. 



Buckinghamshire Mollusca. — On referring to our Journal for conchological 

 records for Bucks. , I only find 33 species recorded and I therefore wish to record 

 the occurrence of Helix virgata, H. itala, H. cantiana, Cyclostoma elegans and 

 Clausilia laminata, all collected by my friend Mr. W. G. Stephenson, of Cheadle, 

 Staffs- , this autumn, near Prince's Risborough and Monk's Risborough in Bucks. 

 The specimens of H. virgata and H, cantiana are both decidedly above the average 

 size. As this county appears to have been somewhat neglected conchologically, I 

 trust some of our members may be able to work up its molluscan fauna. — John R. B. 

 Masefield, Rosehill, Cheadle, Staffordshire, 20th October, 1899 {Read before the 

 Society, Nov. 8th, 1899). 



