234 



1S0Z0IG ZONES. 



the dredge to come up with little else than the frag- 

 ments of branching Bryozoce. 



The species of bivalved Testacea . have a wider 

 distribution than the Gasteropods, but the relative 

 proportions of these two great divisions depend, in 

 every local fauna, on the nature of the coast. It is 

 owing to this cause, according to M. D'Orbigny, that 

 the inequality is so great in the shells of the Cana- 

 ries. These islands are rocky ; hence the number 

 of creeping Gasteropods, whilst of the bivalves a 

 large proportion consists of such as attach them- 

 selves, — street, Chama, Spondylus, &c. 



Both sides of the North Sea, from the Murray 

 Frith to the fiords of Southern Norway, if at any 

 time they should be raised, with their sedimentary 

 deposits, into dry land, would be found, though 

 more than 300 miles apart, to contain an assemblage 

 of marine Testacea specifically identical. 



Over and along the coasts which encircle the 

 Arctic basin, there is also for the northern shores of 

 the Old World and the New a perfect identity of 

 specific forms ; and the same Arctic forms are com- 

 mon to the west coasts of Finmark and the north- 

 east of Greenland. 



The great Mediterranean fauna is distributed 

 with wonderful uniformity, as is also that of the 

 Red Sea. 



Such areas, in respect of the identity of the spe- 

 cies they contain, may be termed Isozoic. 



