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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
long persecution by man. But, as already noted, it extends. or has in former days extended, far up the west coast of America, and is still occasionally found on the coast of California.
SECTION III.- DISTRIBUTION OF SIRENIANS
Only two forms of Sirenians are at the present time existing on the earth's surface—the Manatee (Manatus)
and the Dugong (Halicore)—each representing a distinct family of the Order. The Manatee (Fig. 44, p. 202) is an inhabitant of the coasts and estuaries of both sides of the middle Atlantic Ocean-one species (Manatus senegalensis) occurring on the African shores, and another (M. americanus) on the South American coast and in the Antilles. A third species (M. inunguis), so far as we know at present, is found only in fresh water bigh up the Amazon.
The Dugong (Halicore) (Fig. 45, p. 203) is distributed from East Africa, along the shores of the Indian Ocean and its islands, to North Australia. Three species of this genus have been established—Halicore tabernaculi from the Red Sea, H. dugong from the Indian Ocean, and H. australis from Australia; but it is doubtful how far these forms are actually distinguishable.
Besides Manatus and Halicore, a third quite distinct form of Sirenian was formerly an inhabitant of the North Pacific. This was Steller's Sea-cow (Rhytina stelleri), by far the largest animal of the group, which was exterminated by human agency about 1768. Fortunately recent researches in Behring's Island have been successful in supplying specimens of its skeleton for our principal museums, and Steller, its discoverer, left to posterity a good account of its habits and anatomy.