562 CHORDATA. 
and the male dugongs have a single pair of tusk-like upper 
incisors. The place of front teeth is taken by hard horny 
pads upon the rostrum and mandible. The molar teeth 
have a pair of transverse ridges, like those of the tapir, 
and they succeed each other in series, as in the elephant, 
armadillos and kangaroo. The extant forms are apparently 
monophyodont. The stomach is fairly complex, with at 
least two chambers, and the intestine is long. The 
placental characters are not fully known, but the dugongs 
have a zonary placenta which is non-deciduate. The 
mamme are paired and pectoral in position. At the 
present day the order is limited to a zone between 30° N. 
and 30° S. of the equator. 
Fig. 385.—AMERICAN MANATEE (Manatus Americanus) from life. 
(From Flower and LYDDEKER.) 
Family I.—Manatidz or Manatees.—Three species found in the 
rivers falling into the Atlantic basin. They are peculiar in having only 
six cervical vertebrae. Beneath the horny pads of the jaws are vesti- 
gial incisor teeth # and the molars may be as many as }}. 
Family IJ.—Halicoridz.—The Dugongs are larger and are found 
in the Red Sea, Indian Ocean and Northern Australia. The males 
have incisor tusks which are vestigial in the female. The molars do 
not exceed 8. They are more marine than the Manatees. 
Family III.—Rhytinide.—The Rhytina or Steller’s sea-cow 
was a large sirenian (25 feet) formerly found in the district of Behring 
Island. It was finally exterminated at the hand of man in 1768. This 
species had no teeth, their places being supplied by horny pads. 
Certain fossil forms, such as Halitherium (Miocene), show 
us that the sirenians were abundant at that epoch and even 
