Page:The Zoologist, 4th series, vol 1 (1897).djvu/254

226 tatives of four genera of true Phocidæ: Ogmorhinus, Lobodon, Leptonychotes, and Ommatophoca, which are peculiar to the southern seas, and are quite distinct from all their northern representatives in the Arctic Ocean. The Sea-elephant, Macrorhinus, is also a denizen of Notopelagia, though, as we have already seen, it has wandered north along the South American coast far into Mesirenia.

Like Macrorhinas, Otaria also, containing the group of Eared Seals, appears to have been originally an Antarctic group, and the greater number of its species, although nowadays very much reduced in numbers, are still found in the Southern Ocean. But the Otariæ have travelled still further north than Macrorhinas, and three, if not four, species, as already stated, are in these days well established inhabitants of Arctirenia.

The Sirenians are absent from Notopelagia, but Cetaceans of every kind are abundant. Besides one or more representatives of the true Whalebone Whale, Balæna, Notopelagia has a smaller representative of the group, Neobalæna, entirely restricted to its area. It has also representatives of Megaptera and Balænoptera, though it is doubtful how far they are even specifically distinct from some of their northern representatives.

Among the Toothed Whales, Odontoceti, we find a large Ziphioid form, Berardius, restricted to the Notopelagian area, while Ziphius and Mesoplodon also occur there. The Dolphins, Delphinidæ, are likewise numerous, and present some distinct species, but not, so far as our present knowledge extends, any generic forms that do not occur elsewhere.

But Notopelagia is sufficiently distinguished from all the five more northern sea-regions by possessing four genera of Seals and two of Cetaceans entirely restricted to its area.

It has therefore, I think, been shown that for the geography of marine mammals, the ocean may be most conveniently divided into six Sea-regions, which are as follows:—

I. characterized by its Seals, Phocinæ, of which two genera, Halichœrus and Cystophora, are peculiar,