210 THE GEOGRAPHY OF MAMMALS 



because the Seals and Walrus in the course of time, during 

 unusually mild summers, may have extended themselves 

 along the north coast of the American continent into the 

 Northern Pacific. But Arctirenia, as we shall presently 

 show, is markedly distinguishable from Arctatlantis by 

 the presence of Eared Seals (Otaria), which are utterly 

 unknown in the whole of the Atlantic area. Otaria is in 

 fact, as regards Arctatlantis, a lipomorph. 



The Sirenians are entirely absent from the North 

 Atlantic and constitute another lipomorph of that area. 



Coming to the Whales, we find the Mystacoceti well 

 represented in the North Atlantic by Baliena, Megaptera, 

 and Bal&noptera ; but of these the two latter are almost 

 universally distributed over the ocean, and Balsena recurs 

 again in the North Pacific as well as in more southern 

 latitudes, so that there is no genus of Whalebone Whales 

 peculiar to Arctatlantis. 



Proceeding to the Odontoceti, the case is different. 

 Amongst the Physeteridee, Hyperoodon is confined to 

 Arctatlantis. Arctatlantis therefore may be said to be 

 well characterized by the possession of at least three genera 

 of marine mammals not found elsewhere, viz., Halichcerus, 

 Cystophora, and Hyperoodon, and by the complete absence 

 of the Eared Seals {Otariidas). 



Section VII. — The Mid-Atlantic Sea-region, 

 or Mesatlantis 



Mesatlantis has certainly not so many forms of marine 

 mammals confined to its area as Arctatlantis, but there 

 seem to be good grounds for its separation. As we descend 



