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peds, which are semi-aquatic; (2) the Sirenia, or Manatees, which are mainly aquatic; and (3) the Cetacea, or Whales, which never leave the water, and are wholly aquatic. We will first consider briefly the principal representatives of these three groups, following nearly the arrangement of them employed in Flower and Lydekker's “Mammals Living and Extinct.”
SECTION II.- DISTRIBUTION OF PINNIPEDS
The Pinnipeds, which we will take first, comprise three distinct families—the Otariide, the Trichechidæ, and the Phocidæ. Beginning with the Otariide, or Eared Seals, commonly known as Sea-lions and Sea-bears, we find the greater number of the species confined to the South Polar Ocean, where they pass most of their time at sea, but, as is well known, resort to the land at certain seasons for breeding purposes. In the Atlantic Ocean, so far as is known, the Eared Seals have never been ascertained to occur much further north than the estuary of the La Plata on the American coast, where the Patagonian Sea-lion (Fig. 41, p. 199) is met with, and the vicinity of the Cape on the African coast, where Otaria pusilla is found. But in the Pacific, on the contrary, three distinct species of Otaria are distributed all over the northern portion of that ocean. Two species of Sea-lions are also met with in the Galapagos, and they likewise occur on the coasts of Peru and Chili. I think therefore we may assume that Otaria was originally an Antarctic form, but has travelled northwards along the West-American coast and is now firmly established in the North Pacific. In a parallel way in the Class of Birds, the Albatrosses (Diomedea), which is essentially a group of the Antarctic Seas, are represented by three distinct species in the North Pacific.
The second family of the marine Carnivora, on the other hand, the Walruses (Trichechids), are entirely Arctic in their distribution-one species (Trichechus rosmarus)
(see Fig. 42, p. 200) being peculiar to the North Atlantic, a second nearly allied species (T. obesus) takes its place in the Northern Pacific.
The third family of Pinnipeds is more numerous and varied, both in genera and species, than the two preceding, and has a more extended range. The Seals, Phocids, embracing about nine different generic forms, are most numerous in the Arctic and Antarctic Seas, but are also feebly represented in some intermediate localities. Beginning with the North Atlantic, we find several species of Phoca (Fig. 43, p. 201), inhabiting various parts of this area, and the Grey Seal (Halichorus) and the Bladder-Seal
(Cystophora) exclusively confined to it. In the North Pacific all the four true Seals belong to the genus Phoca, and three of them are identical with the North Atlantic species; but when we descend as far south as the Gulf of California on the American coast we meet with a species of Sea-elephant (Macrorhinus) which, like Otaria, has no doubt penetrated thus far from its ancestral abode in the Antarctic Ocean.
Returning to the central Atlantic we find two species of Seals inhabiting these waters, both belonging to the same genus, Monachus. One of these (M. albiventer) inhabits the Mediterranean and the adjoining coasts of the Atlantic,
while the other (M. tropicalis) is in these days restricted to some of the smaller and less known islands of the West Indies.
The Phocidæ of the Antarctic Ocean all belong to genera distinct from the Arctic forms and more nearly allied to Monachus, the Seal of the Mid-Atlantic. They are of four species, belonging to as many genera : Ogmorhinus, Lobodon, Leptonychotes, and Ommatophoca. Besides these the Sea-elephant of the whalers (Macrorhinus) is essentially an Antarctic form, though now nearly extinct there, after