in 



extreme climates. It ia also necessary to l»ear in mind, that a suitaLle 

 temperature is not the only condition necessary to the existence of 

 animals, and that at the moderate depth (compared with the height of 

 mountains) of 600 fathoms, there must exist total darkness, and a 

 pressure equal to 1-20 times that of our atmosphere, or about 1800 

 pounds to the square inch ; a state of things which we cannot imagine 

 to be very convenient, even if it be not absolutely opposed, to 

 animal existence. 



As the depths of the sea are influenced by climate in an inveree 

 ratio to their distance from the surface, till the point of an unvar^ang 

 temperature is reached, it is evident that difference of latitude must be 

 of much less importance to those beings which inhabit the deep sea, 

 than to shallow water species, and we accordingly find the former to 

 be more extensively distributed than the latter. A considerable vai'ia- 

 tion, as regards the distribution of moUusca, talces place between the 

 opposite sides of the north Atlantic. On the eastern shores, interve.ning 

 between those of the arctic and tropical regions, are two distinct 

 faunas, which have been termed the Celtic, and the Lusitanian or 

 ^lediterrauean ; and these so run into one another, that it would be 

 difficult to fix upon an exact line as the commencement or termination 

 of either of them. On the American shores, species geneiully charac- 

 teristic of the arctic seas extend southward as far as Cape Cod in lat. 

 42° (the parallel of the north of Portugal), where they are said to 

 disappear abruptly, and to be replaced by genera including Pyrnla, 

 Ranella, and Columhella, evidently forms of a more southern type, and 

 which appear to represent those constituting the Lusitanian fauna on 

 this side of the Atlantic. 



Dr. Philippi has appended to his admirable work, on the MoUusca of 

 Sicily, a comparison of the fauna of that country with the faunas of all 

 the principal districts and localities of which there had been any list of 

 shells published. I have considered that it would not be uninstructive 

 to follow his example within a narrower sphere, by comparing 

 together the shells of those parts which I have personally examined 

 and some others of a similar character, with a view of illustrating the 

 range of northern species southward, and likewise of southern species 

 towards the north. I commence with 



Western Scandinavia. 



In a catalogue of the MoUusca of Western Scandinavia, pubUshed 

 by Professor Loven, of Stockholm, there are, after rejecting a few 



