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Lobodon, Leptonychotes, and Ommatophoca. Besides these the Sea-elephant of the whalers (Macrorhinus) is essentially an Antarctic form, though now nearly extinct there, after

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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)

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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. ameri

canus) 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 high 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.

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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.

SECTION IV.-DISTRIBUTION OF CETACEANS

Adopting the recognized division of the Cetaceans into two sub-orders, Mystacoceti and Odontoceti, according as to whether their mouths are furnished with baleen ("whalebone") or teeth, we will first consider the True or Whalebone Whales, which consist of a single family Balænidæ, usually divided into five genera: Balana, Neobalæna, Rhachianectes, Megaptera, and Balanoptera. Of these,

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Balana (Fig. 46, p. 204), Megaptera, and Balaenoptera are almost cosmopolitan-species of them, whether distinct or not is at present more or less uncertain, being met with in nearly every part of the ocean. But Rhachianectes has as yet been ascertained to occur only in the Northern Pacific, and Neobalana in the South Polar Ocean, so that we have in these cases two well-marked local types to deal with.

The Toothed Whales (Odontoceti) are more diversified than the preceding group, and are usually held to embrace at least four existing families besides extinct forms.

The first family, containing the Physeteridæ or SpermWhales, consists of at least six genera, Physeter (Fig. 47, p. 205), Cogia, Hyperoodon, Ziphius, Mesoplodon, and Berardius). Physeter and Cogia are inhabitants of the whole oceanic area between the tropics, extending in certain localities some way beyond them. Hyperoodon is confined to the North Atlantic. Ziphius has an extensive range, and has been found in nearly every part of the ocean. Mesoplodon is also widely distributed, but is apparently more abundant in the Southern Hemisphere. Berardius,

FIG. 48.-THE SEE-SEE.

(Platonista gangetica.)

[Flower and Lyd. Mamm., p. 258. ]

however, so far as we know at present, is restricted to the Pacific Ocean.

The second (existing) family of Toothed Whales contains only the Platanistidæ, or Freshwater Dolphins, which although, in some cases, at the present day entirely fluviatile, must probably have descended from oceanic forms.1 The three known genera are Platanista of the Ganges and Indus (Fig. 48), Inia of the river Amazon, and Pontoporia of the river La Plata; the last form making

1 Sir William Flower ("Whales, Past and Present," Proc. Roy. Inst., x., p. 360, 1883) rather favours the idea of a freshwater origin of the Cetaceans.

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