308 Mammals of Eastern Asia 
DUGONGS AND MANATEES ( ORDER SIRENIA) 
These are large, aquatic mammals that are easily confused 
with some of the smaller whales but may be distinguished by 
the following combination of characters : There is no dorsal fin 
(also true in a few whales and porpoises) ; the nostrils are in- 
variably separate; the two nipples are situated on either side 
behind the arms, never close to the vent as in the whales ; the 
snout, broad, obtuse, and provided with a vertical median an- 
terior groove and paired vertical lateral grooves, is quite unlike 
that of any whale ; the bones of the upper and lower jaws are 
abruptly down-turned before their tips. 
The Order Sirenia contains two distinct types of living rep- 
resentatives : the Old World Dugongs, genus Dugong, and the 
New World (and African) Manatees, genus Manatus. Each 
of these is placed in a separate family, respectively the Du- 
gongidse and the Manatidse. A third family, containing the 
giant Steller's Sea-cow, formerly inhabited the area of the 
Bering Straits but became extinct in about 1768 (Stejneger). 
Dugongs and Manatees are distinguished from each other 
by a number of characters, of which the most obvious is the 
shape of the tail. In Dugong the tail is notched into a pair of 
flukes, but in Manatus it is rounded like a gigantic paddle. Other 
differences include the presence of rudimentary nails on the flip- 
pers of Dugong and their absence in Manatus) the presence of 
enlarged tusks in the male Dugong, and their absence in Manor 
tus. 
The Dugong, Dugong dugong, distributed widely through 
the tropical portions of the Pacific and Indian Oceans, although 
it never penetrates more than a short distance into river estu- 
aries, may be included with the present list of continental mam- 
mals of eastern Asia. The dorsal color is gray-brown, the under- 
pays whitish gray. The smooth skin is sparsely dotted with 
coarse short bristles that are so scanty and inconspicuous as to 
