562 CHORD AT A. 



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 

 mammae 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 [Manattts Americaniis) from life. 

 (From Flower and Lyddeker.) 



Family I. — Manatidae 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 II.— Halicoridae.— 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 f . They are more marine than the Manatees. 



Family III.— Rhytinidae.— 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 Halitheriiim (Miocene), show 

 us that the sirenians were abundant at that epoch and even 



