THE COLOURING OF SHELLS. 42 



n 



Land shells are much influenced, as regards their size, by 

 the temperature, altitude, and abundance of food, of the 

 country in which they are found. Specimens of Helix 

 arbustorum from the Swiss Alps, are not one half the size 

 of those of the neighbourhood of London ; the shells of 

 Helix nemoralis and H. hortensis, found in the last-named 

 locality, are not above two-thirds the size of those which 

 occur in Portugal and in the south of France ; and there is 

 so much difference in size between individuals of Bulimus 

 rosaceus found on the coast and on the mountains of Chili, 

 that the latter have been described as a distinct species 

 under the name of Bulimus chilensis. There would be no 

 difficulty in multiplying examples of the same kind. 



It is not so easy to determine the influence of climate on 

 marine shells, although there is little doubt, from the great dif- 

 ferences of size observable between specimens of the same spe- 

 cies, brought from different localities, that it actually exerts 

 considerable power. Indeed, I have been enabled to mark 

 this difference in some of the shells found on our own coast. 

 The specimens of Littorina petraea found on rocks with a 

 southern exposure near Torquay, are larger than almost any 

 others which I have met with in England ; but the largest 

 of this species that I have seen, occur on the part of the 

 Breakwater at Plymouth next the sea, where they are much 

 exposed to the sun. The latter are twice the size of any that 

 I found on the northern face of that magnificent structure. 



The colouring of many shells evidently depends on the 

 degree of exposure to light, air, heat, and the action of the 

 waves to which they may have been subjected. Thus, 

 among the Patellae and Crepidulae, those which are attached 

 to the stems of Fuci or other round bodies, and are thus 

 exposed on all sides, are of a dull colour, or nearly colour- 

 less. This is well exhibited in the specimen of Patella 

 miniata before referred to, which had changed its place of 

 attachment twice during its growth ; the two portions of the 

 shell formed while the animal was affixed to a flat substance 

 being white, beautifully varied with bright red (the general 

 colour of P. miniata), whilst the central portion of the shell 

 is of a dirty yellow, with a few indistinct, reddish dots, like 

 the ordinary specimens of P. compressa.* In like manner 

 P. pellucida when obtained from the stems of Fuci is of a 

 pale horn colour, whilst the same shell, on the leaves, is 

 of a beautiful purple with longitudinal pale blue lines. 



* Such exposed shells are very rarely bright coloured ; hut a specimen of 

 Patella compressa formerly in the collection of the late Earl of Tankerville, 

 but now in that of Mr. Lincolne, is coloured nearly as brightly as P. miniata. 



