SEA-COWS. 95 



pair of anterior flippers, which they have the power of moving 

 in all directions, no posterior limbs, but broad flattened tails, 

 placed, like those of the Whales, horizontally and not vertically as 

 in fish; skin thick and nearly hairless; only the lips are covered 

 with stiff bristles. 



Their bones generally are extremely dense, massive, and heavy, 

 especially the ribs ; of the posterior pair of limbs only two rudi- 

 mentary pelvic bones remain, but no trace of true limb-bones. 

 The anterior caudal vertebrae have well-marked chevron-bones, 

 and in one genus (Manatus) there are only six cervical vertebra, 

 thus forming one of the very few exceptions to the general Mam- 

 malian number of seven. The fore limbs are developed into flat 

 flippers, not showing externally any trace of fingers. 



The skull is of a very peculiar shape and structure, the anterior 

 part of both jaws being bent downwards nearly vertically. The 

 molars are either absent, or very simple square teeth with transverse 

 ridges, suitable for chewing water-weeds and other vegetable sub- 

 stances. The nasal opening, as in the Elephants, is placed very 

 far back on the upper surface. 



The Sirenia consist of three genera, one of which is generally 

 believed to have been recently exterminated : 



(1) Manatus, the Manatees, with eleven molars on each side, 

 of which about six are present at any one time ; snout but little 

 bent downwards ; tail depressed and rounded, its posterior edge 

 forming a semicircle ; rudimentary nails on the flippers. The 

 Manatees, so called from their using their flippers to a slight 

 extent as hands (manus), are natives of the rivers and shores of 

 Eastern America and Western Africa within the tropics, never 

 straying far out to sea, but yet quite unable to go on to the land 

 itself, their whole lives being passed in the water. There are 

 said to be three species of Manatee, namely: the African Manatee 

 (M. senegalensis) ; and two American, the Florida and South- 

 American species (M. latirostris and americanus). 



Stuffed specimens and skeletons of Manatus senegalensis and 

 americanus are placed in the Saloon, and several skulls in [Case 23.1 

 Case 23, Div. B. 



(2) Halicore, the Dugongs, with two tusk-like incisors, and 

 five or six molars on each side; snout bent nearly vertically 

 downwards ; no nails on the flippers ; tail broad, with the poste- 



