DISTRIBUTION OF MARINE MAMMALIA. 225 



nectes glancus, of Cope, which in these days is confined to the 

 North Pacific, and does not range farther south than 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 Rhachianectes, Balcena, Megaptera, and 

 BaUenoptera are all represented in the North Pacific, and also 

 many species of Delphinidce 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 Pacific 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, Macrorhinus, has apparently 

 in former ages travelled up the South American shores and 

 established itself as far north on the coast of California as about 

 34° N. lat. The California Sea-elephant has been discriminated 

 by Gill as a distinct species, Macrorhinus angustirostris, 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, Balcenoptera, Physeter, Cogia, and Ziphius 

 certainly occur there, besides many representatives of the widely 

 spread Delphinidce. 



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 represen- 



