nectes glaucus, 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, Balæna, Megaptera, and Balænoptera are all represented in the North Pacific, and also many species of Delphinidæ 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, Balænoptera, Physeter, Cogia, and Ziphius certainly occur there, besides many representatives of the widely spread Delphinidæ.
XI. 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-
