216 GEOLOGICAL DISTEIBUTION. 



case; and if further or more convincing proof were needed, we 

 have the fact, made pregnant by the recent deep-sea dredgings, 

 that many of the forms contributing to the surface faunas of the 

 north, and hitherto recognised as being essentially northern, are in 

 reality inhabitants of the southern zone as well, only that they here 

 constitute a part of the deep-sea (cold water) fauna instead of the 

 more superficial one. ZSTaturalists have been in the habit of recog- 

 nising four or more distinct zoological provinces along either border 

 of the Atlantic, each one characterised by a more or less well-marked 

 assemblage of animal species ; and about an equal number of such 

 provinces have been assigned to the Pacific littoral. In all these 

 pro vinces^Che' admixture of forms belonging either north or south, 

 it must be admitted, is very great, so much so aa to render the 

 drawing of a line of division a matter of the utmost difficulty; 

 nevertheless, taken in their entirety, the faunas are sufficiently dis- 

 tinct, and serve to mark the climatic influences which limit dis- 

 tribution. Of some five hundred and sixty-nine species of MoUusca 

 recognised by Fischer, in 1878, as occurring on the Atlantic shores 

 of France, no less than four hundred and twenty-seven, or seventy- 

 five per cent., also belong to the British coast, and about an equal 

 number to the Mediterranean.'" On the other hand, of three 

 hundred and fifty- thtee species obtained by M 'Andrew from the 

 southern coast of the Iberian Peninsula, only fifty-one per cent, 

 were common to Britain, and a much smaller number, twenty-eight 

 per cent., to Norway." The moUuscan fauna of the Canary Isl- 

 ands numbers about three hundred species, of which sixty-three per 

 cent, belong to the coasts of Spain and the Mediterranean, thirty- 

 two per cent, to Britain, and seventeen per cent, to Norway. The 

 relation existing between northern and southern, or cold and warm 

 water, faunas is perhaps still better marked on the Western Atlantic 

 border. Thus, of a total of about three hundred species of moUusks 

 belonging to the " Transatlantic .Province " — i. e., the eastern coast 

 of the United States included between Florida and Cape Cod— only 

 sixty recur north of the peninsula of Cape Cod. Again, of seventy- 

 nine species of shells collected by D'Orbigny from the coast of North- 

 ern Patagonia only twenty-seven were common to Uruguay and 

 Brazil. The rich molluscan fauna of the Japanese Archipelago, com- 

 prising four hundred and twenty-nine species, has only one hundred 

 and eighty-five representatives in the Chinese and Philippine waters. 



