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 form; there appears to be but a single species, though more than one name has been given to supposed distinct species. As already mentioned, it differs from the Manatee in the possession of a Whale-like tail; the nostrils, too, are more upon the upper surface of the head, and there are no nails upon the flipper. The peculiar cleft lip of the Manatee is not so well developed in the Dugong, but there are traces of it; and in the foetus the likeness to the Manatee in this respect is very striking. It would thus appear that Halicore is a stage in advance upon Manatus; that the remarkable mechanism of the lip of the latter has been possessed, but has been lost, by the Dugong. The skull of the Dugong is distinguished by the stout premaxillary bones, which bear a tusk in the male. In the female the tooth is there, but is lodged within the bone. This incisor has a milk forerunner. The back teeth of the Dugong (there are no canines) are few in number (four or five, even six), thus showing a gradual reduction when compared with Manatus; and this culminates in the toothless Rhytina. It is also interesting to notice that in the massive lower jaw there are traces of an incisor. Were this to be developed into a tusk, the jaw would present a curious resemblance to that of Dinotherium.

The Dugong, H. dugong, has the reputation of being the original of the mermaid legends, since the young is held to the pectorally-situated breast with one flipper. "But it should be remembered," justly observes Dr. Blanford, "that stories of beings half man or woman, half fish, are as common in temperate as in tropical seas, and that some of them are more ancient than any European knowledge of the Dugong."

Extinct Sirenians.—The earliest genus that can be with certainty referred to this order is the Oligocene Prorastoma. This genus, though offering no particular skull-characters that assist in the determination of the much-debated affinities of the Sirenia, shows a remarkable condition of the teeth that may afford a clue. The species P. veronense, recently described by Mr. Lydekker, is founded upon a fragment of the skull which contains two teeth apparently representing the third and fourth upper milk molars. The interest attaching to these teeth lies in the fact that they clearly exhibit the buno-selenodont condition characteristic of certain early Artiodactyles, e.g. Merycopotamus.

Halitherium is a later genus, which is known by the nearly