DISTRIBUTION OF MARINE MAMMALIA. 227 



whilst Phoca is common to it and Arctirenia ; by the absence of 

 Sirenians ; and by the possession of three peculiar genera of 

 Cetaceans, Hyperoodon, Delphinap terns, and Monodon. 



II. Regio Mesatlantica, sole possessor of the Monk Seal, 

 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 Arct- 

 atlantica, but having tar la also ; the home of the (now extinct) 

 Sirenian Rhytina and of the endemic Cetacean Rhachianectes. 



V. Regio Mesirenica, without true Seals, Phocince, but 

 having Otaria and Macrorhinus from the south; no Sirenian 

 known. 



VI. Riigio Notopelagica, characterized by four endemic 

 genera of Phocidce, and by the presence of many tar ice ; without 

 Sirenians, but with two endemic forms of Cetaceans, Neobalcena, 

 and Berardius. 



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 Macrorhinus, quite unknown in the Atlantic, extend 

 themselves to the northern extremity of the Pacific, the former 

 pervading that ocean up to Behring'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 which did not 

 exist in the Pacific to stop their progress northwards. The only 

 barrier I 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 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 



