212 THE GEOGRAPHY OF MAMMALS 



Indopelagia. As regards the Whales of Indopelagia, we 

 know that Physeter, Cogia, and Ziphius, and numerous 

 forms of Delphinidas occur there, but are not aware of any- 

 Cetacean that is entirely restricted to this Sea-region. 



Section IX. — The North Pacific Sea-region, 

 or Arctirenia 



As was pointed out when speaking of Arctatlantis, 

 Arctirenia has one genus of Phocidse {Phoca) in common 

 with the North Atlantic, and three of the species of this 

 genus appear to be actually identical in these two Sea- 

 regions, whilst a fourth Phoca (P. fasciata) is only found 

 in the North Pacific. The Walrus (Trichechus) is again 

 a form of marine mammals common to both the great 

 northern Sea-regions. But the feature of Pinnipedian life 

 that absolutely distinguishes Arctirenia from Arctatlantis 

 is the presence in the former of three (if not four) well- 

 marked species of the Eared Seals (Otariidte), which are 

 absolutely unknown in the vast extent of the Atlantic 

 down at least to 30° S. lat. 



Arctirenia has unfortunately lost its Sirenian, Steller's 

 Sea-cow (Rhytina stelleri), the largest modern represen- 

 tative of this formerly prevalent group, which since the 

 days of the Pleistocene has greatly diminished in numbers, 

 but I think we may still treat Rhytina as one of the 

 characteristic forms of the Arctirenian Sea-region. The 

 North Pacific is also, even at the present day, the sole 

 possessor of a remarkable genus of Whalebone Whales 

 which combines the long head and elongate form of Balse- 

 onptera with the absence of the dorsal fin of Balssna. 



