Distribution of Marine Mammalia. 271 



Arctirenia has unfortunately lost its Sirenian, Steller's Sea-cow 

 (Ehytina Stelleri), the largest and finest modern representative of this 

 formerly prevalent group, which since the days of the Pleistocene 

 has greatly diminished in numbers, but I think we may still treat 

 Bhytina 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 Balmnoftera with the 

 smooth skin of the throat and absence of the dorsal fin of Balcena} 

 This is the Grey Whale, Rhachianectes glaucus of Cope, which, in 

 these days, is confined to the North Pacific, and does not range 

 farther south that the 20th parallel in that ocean. At the same time 

 it should be stated that indications have been discovered that 

 a nearly allied form existed in the Atlantic in previous geological 

 ages, though this is by no means certain. Besides Rhachianecfes, 

 Balcena, Megaptera, and Balxnoptera are all represented in the North 

 Pacific, and also many species of Delphinidae, of which little is at 

 present known. But Rhytina and Rhachianectes are the only genera 

 of Marine Mammals absolutely confined to Arctirenia. 



X. The Middle Baclfic Sea-region, or Mesirenia. — The Eared Seals, 

 Otaria, must have necessarily passed through Mesirenia in their 

 passage from south to north, though the only record of their recent 

 presence in the central part of the Pacific is, so far as I know, the 

 report that they were formerly found in the Galapagos. It should 

 be stated, however, that Tschudi records the occurrence of two 

 species of Otaria on the islands of the coast of Peru, and that in 

 1802 Humboldt met with an Eared Seal on the Island of San 

 Lorenzo, in the Bay of Callao, which is only some 12° south of the 

 Equator. 



Like Otaria, the Sea-elephant [Mn crorhiniis) has apparently in 

 former ages travelled up the South American shores and established 

 itself as far north on the coast of California at about 34° N. lat. 

 The Californian Sea-elephant has been discriminated by Gill as 

 a distinct species (MacrorMnus angtistirostris) , but its differences 

 from the southern form (M. leoninus) seem to be but trifling. 



As regards the Cetaceans of Mesirenia, our information is at 

 present very imperfect, and I have little to say except that species 

 of Megaptera, Balanoptern, Physeter, Cogia, and Ziphius certainly 

 occur there, besides many representatives of the widely-spread 

 Delphinidge. 



XL The Southern Polar Sea-region, or Notopelagia. — The wide 

 ocean which surrounds the Southern Pole on every side, and extends 

 up to 40° S. lat., seems to present, as regards its marine mammals, 

 a nearly homogeneous fauna, which we will now briefly consider. 

 In the first place it contains representatives of four genera of true 

 Phocidse — Ogmorhinus, Lobodon, Leptonychotes,^ and Oinmatophoca, 



1 Flower and Lydekker, " Mammals," p. 241. 



'^ This generic term, established by Gill in 1872, seems to take precedence of 

 Fcecilophoca, proposed by Flower and Lydekker for the same type (Z. Weddelli) in 

 1891. Cf. Allen, "North American Pinnipeds," p. 418. 



