without food, (properties which, as admirably adapting them for a sea stock 

 upon loug voyages, are extensively taken advantage of for that purpose 

 by sailors of the south of Europe ; and I may here remark, that as an 

 article of food, the moUusca, with very few exceptions, have been too 

 much neglected by ourselves, and that snails ai'e not only wholesome 

 and nutritious, but even, where prejudices do not interfere, esteemed a 

 delicacy, not to mention that their being in request for culinary purposes 

 would be the means of relieving our gardens from their inroads) ; 

 notwithstanding, I say, their powers of endurance, they appear to be 

 particular in the selection of locality. The arctic climate and productions 

 are evidently not suited to snailish and sluggish habits and tastes. Even 

 in the colder temperate regions species are few, but increase in numbers 

 as we proceed southward, and they are found particularly to abound in 

 limestone formations. 



It is a most remarkable fact connected with the distribution of laud 

 shells, that some species are extended over very wide districts, while 

 others are restricted to an area of a few square miles, or even less. 

 Great Britain does not offer for observation a single species which is 

 not likewise an inhabitant of France or Germany, though the neigh- 

 bouiing countries of the continent possess some which are not to be met 

 with in this kingdom ; and while thus among the hundreds of islands of 

 Great Britain not one produces a species peculiar to itself, in the groups 

 of the Canaries, Madeiras, and Azores, each island presents some 

 species supposed to be strictly local. 



This fact is particularly striking in the Madeiras — where Madeii'a 

 proper contains but few species, while the small island of Porto Santo 

 supplies an astonishing number, in general specifically distinct from 

 those of Madeira, and the rocky islets called the Desertas, with diffi- 

 culty accessible by man, have each some peculiar forms and in great 

 abundance. 



These facts seem to indicate that Great Britain and Ireland, includ- 

 ing the Hebrides, Orkney, Zetland Islands, &c., have at one time 

 formed part of the European continent, but that the more distant 

 islands which I have named — raised by volcanic action from the depths 

 of the Atlantic, have been each the scene of the creation of certain 

 species which have been confined within their narrow limits by the 

 Burromiding sea. 



Opposed to this idea is the fact already alluded to, that some marine 

 littoral species, I may particularly mention Littorina striata, are com- 

 mon to West Africa, tlie Canaries, Madeira, and the Azores, which (as 

 it is quite impossible for littoral pliytophagous animals to have travelled 



