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.

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, Neobalana, Rhachianectes, Megaptera, and Balaenoptera. Of these,

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 Neobalena 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 Physeterida 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.

(Platanista 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.

a connecting link between the two preceding genera and the marine Dolphins.

The third family of Toothed Whales, containing the Dolphins, Delphinidæ, is very numerous in species and embraces at least fifteen or sixteen genera, of which the Common Dolphin (Fig. 49) is a good example. But in spite of the efforts of Mr. True, who has recently given us an excellent summary of our present knowledge of them,1 both the genera and species of Delphinidæ are still so imperfectly understood that not much can be said about their geographical distribution. Most of the forms

FIG. 49. THE COMMON DOLPHIN.

(Delphinus delphis.)

[Flower and Lyd. Mamm., p. 271.]

appear to be very widely distributed, but it may be said generally that Dolphins are most abundant in the intertropical seas and less plentiful both to the north and south of them.

There are, however, two forms that are exclusively inhabitants of the Northern Oceans. These are the very remarkable Narwhal (Monodon), in which the male is furnished with a single enormous horn-like tusk, and the Beluga, or White Whale (Delphinapterus), closely allied

1 See "A Review of the Family Delphinidæ," by Frederick W. True. Bull. U.S. Nat. Mus., No. 36 (Washington, U.S., 1889).

to the Narwhal in many points of its general structure (Fig. 50). These may be looked upon as quite isolated

FIG. 50.-THE BELUGA.

(Delphinapterus leucas.)

[Flower and Lyd. Mamm., p. 262.]

forms characteristic of the Arctic portion of the Atlantic and Pacific.

SECTION V.-DIVISION OF THE MARINE AREA OF THE GLOBE INTO SEA-REGIONS

From what has been already said, it will be evident that although many of the marine mammals have a wide distribution, others are very definitely localized; and a study of the latter will enable us to divide the oceanic portion of the globe into six Sea-regions, corresponding to a certain extent with the six Land-regions already discussed. It is proposed to name these Sea-regions, which are shown in the map (Plate VIII., p. 216), as follows:

=

(1) The North Atlantic Sea-region, or Arctatlantis (aρKтоs and 'ATλavTis the daughter of Atlas), consisting (ἄρκτος 'Ατλαντὶς of the northern portion of the Atlantic down to about 40° N. lat.

(2) The Mid-Atlantic Sea-region, or Mesatlantis (μéoos and 'ATλavTis), consisting of the middle portion of the Atlantic down to about the Tropic of Capricorn.