i62 ' The Post-Pliocene Non-Marine Mollusca of Ireland.' 



Ferussac's illustrations. If the shells do thus agree, then 

 they are not V. hihernica, and if they do not, the name pyrenaica 

 cannot be used for such shells. If the anatomy and shells of 

 Mr. Bowell's so-caUed V . pyrenaica agree with the anatomy 

 and shells of V. hihernica, as Kennard and Woodward imply, 

 then they are not the V . pyrenaica Fer., and the V . pyrenaica 

 of Bowell merges into the synonymy of V. hihernica Taylor. 



Further, Moquin-Tandon's figure of the animal does not, as 

 stated by Kennard and Woodward, agree either with my figures 

 or description, and in addition the confirmatory sign ( !) is 

 not used by him for the purpose erroneously stated by them, 

 for he expressly explains that the sign is used to indicate when 

 he has himself seen specimens from the actual authors of the 

 various statements of localities, etc. This mark nowhere 

 appears in his account of V. pyrenaica, and he gives no localities 

 therefor, except those of Partiot and Ferussac, and both lack 

 his mark of verification. 



Under the heading of Helix aspersa, Kennard and Woodward 

 say ' Mr. Taylor remarks that Helix aspersa tends to produce 

 a thicker shell than usual when living near the sea shore.' In 

 reference to this, I may say that this is not, as erroneously 

 stated by them, a personal observation, but a summary of the 

 experience of others, and gives the station where incrassation 

 has been observed, without prejudging the precise cause to 

 which shell-thickening was due. The authors, however, say 

 that ' the proximity of the sea has no direct bearing on the 

 thickness of the shell,' though acknowledging that ' extremely 

 heavy shells do occur near the sea,' which they ascribe to the 

 presence of foraminiferous sand. The incrassation of the shell 

 is, however, primarily dependent on the selective physiological 

 action of the organs of the animal, the secretion of shell sub- 

 stance being a common property of the Mollusca, varying in 

 efficiency in different species, as well as to some extent among 

 individuals of the same species ; thus Unio margaritifer secretes 

 a thick and heavy calcareous shell when living in granitic 

 streams, where lime is not plentiful and where LimncecB and 

 Ancyli produce thin and fragile ones. Further, although we 

 may naturally expect to find thick and heavy shells where 

 lime IS plentiful, and fragile ones where it is scarce, yet the 

 heaviest specimen of Helix aspersa in my collection, which, 

 though of ordinary size, weighs 129 grains, was found by Mr! 

 J. Davy Dean, of the National Museum of Wales, upon Mill- 

 stone-grit at Caton, Lancaster, where lime was very deficient. 



For the purpose of studying Geographical Distribution, 

 the authors divide the species into three groups : (i) a Western 

 or ancient group ; (2) a Germanic or modern group, and (3) a 

 group of uncertain origin but probably Holarctic. The Ger- 

 manic group the authors restrict to comparatively few — about 



Naturali.'t, 



