22 



POPULAR CONCHOLOGY. 



different individuals, influenced undoubtedly by 

 favourable or unfavourable situations, and 

 abundance or scarcity of food. But this opinion 

 can only be satisfactorily proved or disproved 

 when shells are better known. Mr. Gray has 

 the following remarks on the subject : — " The 

 thickness, roughness, or smoothness of shells ap- 

 pears to depend in a great degree on the still- 

 ness or agitation of the water which they in- 

 habit. Two specimens of the same species of 

 shell will often be found very different in ap- 

 pearance, according to the situation in which 

 they have been placed. For instance, the 

 common Buccinum of our coast is thick, solid, 

 and heavy, when found in a rough sea, and 

 thin, light, and smooth, when found in the 

 still water of harbours. Boring shells are 

 generally influenced in regard to their size, 

 thickness, and form, by the hardness or soft- 

 ness of the rock in which they are found. 

 Land shells are much influenced, as regards 

 their size, by their temperature, altitude, and 

 abundance of food. The shells of Helix ne- 

 moralise and Helix hortensis found near Lon- 

 don, are not above two thirds of the size of 



