Order SIRENIA. 



The Manatees and Dugongs, formerly classed with the Cetacea, 

 and subsequently assigned by De Blainville and others to the Un- 

 gulata (or Pachydermata), are now placed in a separate order, 

 the Sirenia, which has certainly no affinity to Cetaceans and very 

 little, if any, to Ungulates. The Sirenia resemble Cetacea in their 

 fish-like form, in the absence of external hind limbs and of a 

 distinct sacrum, and in the rudimentary condition of the pelvis, in 

 the horizontal expansion of the tail to form a swimming organ, in 

 the pectoral limbs being converted into paddles without separate 

 digits, in the small eyes, and in the want of an ear-conch. On the 

 other hand, the head is of moderate size and rounded, the nostrils 

 are always separate, valvular, and anteriorly situated, the mouth 

 small and the teeth, in all living forms, of two kinds, incisors and 

 molars ; there is no dorsal fin ; and hairs or bristles occur on the 

 lips at all ages and are sometimes scattered over the body. The 

 muzzle is truncated, and horny plates, doubtless used in mastication, 

 are developed on the anterior portion of the palate and of the lower 

 jaw. 



The bones are dense and massive. The skull is peculiarly formed, 

 but very unlike that of any Cetacean. The anterior narial aperture 

 is large and high in position, and the nasal bones are generally 

 wanting in living forms. There is a thick rostrum, chiefly formed 

 by the premaxillaries. The flat ends of the bodies of the vertebrae 

 do not ossify separately, as in nearly all other mammals. The 

 radius and ulna are generally united together at both ends. The 

 digits are five in number, and the phalanges, which are never more 

 numerous than in ordinary Mammalia, are flattened. The stomach 

 is compound, the intestines long, and there is a caecum. The 

 testes are abdominal, the uterus bicornuate, and the placenta non- 

 deciduous and diffuse. The mammas are two in number and are 

 pectoral and postaxillary. 



The order contains only one family and two living genera, which 

 are purely herbivorous, feeding on aquatic plants, and which inhabit 

 shallow seas, estuaries, and rivers. They are never found out at 

 sea, like Cetacea, nor do they ever voluntarily go ashore. 



Family 



Characters of the order. Of the two living genera one, Manaius, 

 is found in rivers and estuaries on both sides of the tropical At- 

 lantic, the other, HaUcore, inhabits the coasts of the Indian Ocean. 



