XI THE DUGONG 337 
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 lp 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 
1 Proc. Zool. Soc. 1892, p. 77. 
WO: XS Z 
