216 THE GEOGRAPHY OF MAMMALS 



Seals, Monachus, amongst the Pinnipeds, and of the 

 Sirenian genus Manatus. 



III. Regio Indopelagica, characterized by the presence 

 of the Sirenian Halicore and by the absence of Pinnipeds. 



IV. Regio Arctirenica, with Phoca like the Regio 

 Arctatlantica, but having Otaria also; the home of the 

 (now extinct) Sirenian Rhytina and of the endemic Cetacean 

 Rhachianectes. 



V. Regio Mesirenica, without true Seals (Phocinte), but 

 having Otaria and Macrorhinus from the south ; no 

 Sirenian being known there. 



VI. Regio Notopelagica, characterized by four endemic 

 genera of Phocidse, and by the presence of many Otaria ; 

 without Sirenians, but with two endemic forms of 

 Cetaceans (Neobal&na and Berardius). 



In conclusion, attention may be called to some of the 

 more remarkable 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 Macrorhinus, quite unknown 

 in the Atlantic, extend themselves to the northern ex- 

 tremity of the Pacific, the former pervading that ocean 

 up to Behring's Strait, and the latter reaching to the 

 Californian coast. It follows that in former ages there 

 must have been some barrier in the Atlantic which did 

 not exist in the Pacific to stop their progress northwards. 

 The only barrier one can imagine that would have effected 

 this must have been a land uniting South America and 

 Africa, across which they could not travel. Adopting 

 this hypothesis, we have at the same time an explanation 

 of the presence of the Manatee on both the American 



