and εἰρήνη=pax), containing the northern portion of the Pacific Ocean down to about the Tropic of Cancer.
(5) The Mid-Pacific Sea-region or Mesirenia (μέσος and εἰρήνη), containing the inter-tropical portion of the Pacific Ocean; and finally
(0) The Southern Sea-region or Notopelagia (νότος and πέλαγος), containing the whole of the South Polar Ocean all round the globe south of the above-mentioned limits.
We will now proceed to consider shortly the characteristic mammals of these six sea-regions.
VI. The North Atlantic Sea-region, or Arctatlantis.
Amongst the Pinnipeds two well-marked generic forms, the Grey Seal, Halichœrus, and the Bladder Seal, Cystophora, are exclusively confined to Arctatlantis. The True Seals, Phoca, and the Walrus, Trichechus, are found in this region and in Arctirenia; and of the former genus three species—P. vitulina, P. grœnlandica, and P. barbata—are actually common to both these sea-regions, while the Walruses—Trichechus rosmarus and T. obesus—of the two sea-regions are perhaps somewhat doubtfully distinguishable. It may be easily understood how this has come to pass, because the Seals and Walrus may in the course of time, during unusually mild summers, 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, what I have called on previous occasions (see P.Z.S. 1882, p. 311) a "lipotype" of Arctatlantis, but what I now propose to designate a "lipomorph."[1]
- ↑ On former occasions I have used the term "lipotype" for a natural group which characterises a particular locality by its absence. It would, however, perhaps be better to change the term to "lipomorph," because the type and its compounds have been generally employed in reference to the particular specimens of a species upon which original descriptions are based (cf. Thomas, P.Z.S. 1893, p. 241). In the same way a natural group which characterises a particular country may be called a "topomorph" (τόπος, locus, and μορφή, forma). Thus, in Africa Giraffa and Phacochœrus would be "topomorphs," and Cervus and Ursus would be "lipomorphs."
