SIRENIA. 571 



The Manatees are characterised by the possession of nume- 



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rous molar teeth( - -) and of two small upper incisors, which 



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are wanting in the adult. The tail-fin is oblong or oval in 

 shape, and the anterior limbs are furnished with nails to the 

 four outer digits. They occur on the east coast of North 

 America, especially in the Gulf of Mexico, and another species 

 is found on the west coast of Africa. They are generally found 

 in considerable numbers about the mouths of rivers and estu- 

 aries, and they appear to live entirely upon sea-weeds, aquatic 

 plants, or the littoral vegetation. They are large, awkward 



Fig. 243. Sirenia. Dugong {Halicore). 



animals, attaining a length of from eight to ten feet as a rule, 

 but sometimes growing to a length of nearly twenty feet. 



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The Dugongs (Halicore, fig. 243) have - - molar teeth in 



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the young condition, but only - when old. Inferior incis- 

 ors are present in the young animal, but are wanting in the 

 adult. The upper jaw carries two permanent incisors, which 

 are entirely concealed in the jaw in the females, but which 

 increase in size in the males with the age of the animal, till 

 they become pointed tusks. The anterior extremities are nail- 

 less, and the tail-fin is crescentic in shape. In their general 

 appearance and in their habits the Dugongs differ little from 

 the Manatees, and they are often killed and eaten. They 

 attain a length of from eight to ten, twelve, or more feet, and 

 are found chiefly on the coasts of the Indian Ocean. The bones 

 are remarkable for their extreme density, their texture being 

 nearly as close as ivory. 



The Manatees and Dugongs, as before said, are the only 

 living Sirenia ; but besides these there is a very singular form, 

 the Rhytina Stelleri^ which is now extinct, having been exter- 

 minated by man within a comparatively recent period. This 



