66 THE ZOOLOGIST. 



There are several small points which seem to indicate a more 

 elaborate ancestral shell to some of our species : for instance, the 

 embryo hairs on Paludina vivipara,* and Planorbis co7*neus,\ the 

 occasional reversion to a banded form of Limncea peregral and 

 Bidlirus hypnorum. Among the land forms, I fancy the peripheral 

 band and embryonic hairs which occur in Fruticicola rufescens, 

 F. cantiana, &c, have the same significance. 



It is possible that Limncea may be adventitiously protected by 

 the thick growth of weed§ which so often covers the shell. 



To turn to terrestrial forms : here we find two great main 

 divisions of coloration — (A) oligochromatic approaching polychro- 

 matic, as in Tachea, &c. ; (B) monochromatic, the prevailing form. 



Of the former class two explanations are possible : (1) They 

 have retained the pigmented shells which were of use to them in 

 the sea. But this is rendered improbable because (a) the colours 

 which were of use to them in their marine habitat would probably 

 be useless || on land; and (/?) the colours would hardly have 

 remained the same while their internal organisation was under- 

 going such extensive modifications. (2) They have acquired 

 their colours, the migrating species having been either coloured or 

 uncoloured. This view I think is alone tenable. 



The monochromatic species (if descended from coloured forms) 

 have become so for the same reason as Limncea ; the life they 

 lead is distinctly quiet and retired. The brightly coloured species 

 all live a more exposed life (as one might expect) than the dull 

 ones. Genera like Hyalinia live under stones, among dead 

 leaves, &c, and by no means court a bright light. Bright places, 

 too, are generally too dry for them. 



The two groups may likewise be distinguished, I think, by 

 their hybernation. Group A is characteristic of a warmer climate 

 than group B, which is essentially boreal. Tachea and Cryptom- 



* J. S. Kingsley ('Kiverside Natural History,' vol. i. p. 341, fig. 432) 

 figures a half -grown specimen, with bands and rows of upright spines; in 

 error apparently. 



f For a figure, see J. W. Taylor's « Monograph British Land and Fresh- 

 water Shells,' vol. i. p. 74. 



I This may be pathological : J. W. Taylor, op. cit. i. p. 102. 

 § Cf Poulton, op. cit. p. 77. 



II Of course the colours may be at present useless, but this appears im- 

 probable* 



