SHELL-COLORATION IN BRITISH EXTRA-MARINE MOLLUSCA. 07 



phalus, e.g. hybernate very rigidly through a winter however mild; 

 while Hyalinia, Fruticicola rufescens and hispida, and especially 

 Vitri7ia (to give a few examples only), keep fairly lively all through 

 the winter.* 



Certain species (Bullminiis obscurus, e.g., and " Helix " obtecta, 

 from Madeira), though monochromatic, have been supposed in 

 their younger stage to practice concealment by coating their 

 shells with small particles of dirt ; but doubt has recently been 

 thrown on this idea, and the coating may well be accidental. 



Among the coloured species, one group may easily be separated 

 off : the black and white shells of Xerophila and Cochlicella. This 

 form is one essentially frequenting dry heaths, &c. S. S. Pearce 

 thinks that some forms of this group (X. caperata, var. omata) may 

 be sematic, and warn the sheep, which frequent its habitat, that it 

 is not very palatable ;t but there used to be an idea that South- 

 down mutton owned its delicate flavour to this strange diet. I 

 However, taking into consideration the fact that nearly all desert 

 shells show a tendency towards leucochroism, I am inclined to 

 attribute their pale, opaque coloration to the fact, that they are 

 hence more able to withstand the great changes of temperature to 

 which their open habits must expose them.§ Indeed, Bouchard- 

 Chantereaux states that X. virgata never hybernates, and does 

 not seem to mind the cold ; and it must be remembered that 

 extensive, dry areas, if very hot in the daytime, at night are 

 extremely cold. || I suspect that Xerophila may be, in part, 

 cryptically coloured. It is my experience, at any rate, that how- 

 ever much the collector knows the shape, size, and colour of the 

 species he is looking for, or however plentiful they may be, till he 

 catches sight of one, the ground looks quite fruitless ; when one 



* E. Ehmner, op. cit. pp. 96, 131; A. H. Gooke, op. cit. p. 24. Quite 

 recently, after two very sharp frosts, and while there was ice on all the 

 ponds, I found H. nitidula, Patala rotundata, and F. hispida, iu abun- 

 dance, crawling freely on the under surface of a large stone tilted up 

 against a shed on a very exposed hill. 



f ' Journal of Conchology,' vi. p. 123 ; ' Cambridge Nat. Hist.' iii. p. 89. 



I Borlase seems to be the originator of this statement, cf. Harting, 

 'Eambles in Search of Shells,' pp. 75, 76. — Ed. 



§ See Poulton, op. cit. pp. 16, 17. 



il I have seen X. caperata, crawling over moss when snow was quite thick 

 on the ground. 



