358 Olf THE TJISTRIBUTIOV OF MARINE MAMMALS. [Mar. 16, 



In conclusion, I will call attention to some of the more remark- 

 able points in the general distribution of the marine Mammals 

 and to their apparent significance. 



In the first place it is evident that the Pacific has much more in 

 common with the Notopelagian region than the Atlantic. Otaria 

 and JIaci-orhinus, quite unknown in the Atlantic, extend them- 

 selves to the northern extremity of the Pacific, the former per- 

 vading that ocean up to Bering's Straits, and the latter reaching 

 to the Californian coast. It follows that in former ages there must 

 have been some barrier in the Atlantic whicli did not exist in the 

 Pacific to stop their progress northwards. The only barrier I can 

 imagine that w^ould have efi'ected this must ha-\e been a land 

 uniting S. America and Africa, across which they could not travel. 

 Adopting this liypothesis, we have at the same time an explanation 

 of the presence of the Manatee on both the American and African 

 coasts. The Manatee could hardly live to cross the Atlantic. It 

 is only found close to the coast, where it browses on sea-weeds and 

 other vegetable food in shallow water. How did it travel from 

 America to Africa (or vice versa), unless there were a continuous 

 shore-line between them ? The same may be said of the Monk- 

 Seal (Monachus), of which one species lives in the Mediterranean 

 and on the African coast and islands and another in the "West 

 Indies. We can hardly believe that these creatures could easily 

 traverse the whole Atlantic. The hypothesis of a former barrier 

 of land between Africa and America, which we know is sup- 

 ported by other facts of distribution ', would alone explain the 

 difficulty. 



On the other hand, in the Pacific we find no such break between 

 the north and south. The aquatic Mammals of Notopelagia have 

 evidently had free access to the whole of the Pacific for a long period 

 and have well availed themselves of this facility. 



Again, while the great Southern Ocean exhibits a considerable 

 uniformity of marine Mammalian life, we see the Northern waters 

 di\-ided into two distinctly recognizable Eegions by the interposed 

 masses of land. All these facts, with the one exception of the 

 supposed Atlantic Barrier, would tend in favour of the now 

 generally accepted doctrine that the principal masses of land and 

 water are not of modern origin, but have existed mainly in their 

 present shapes throughout all ages. 



TOPOMORPHS OF THE SlX SeA-BEGIONS. 



I. Arctatlantis. IV. Arctirekia. 



Halichcenis. Otaria. 



Cystophora. 



Rliytina. 



Hyperoodon. Ehachianectes. 



1 Cf. Wallace, Geogr. Distrib. vol. i. p. 156. 



o 



