Dr. J. E. Gray on the Species of Manatees, 135 



lower jaw flat, with a central, large, conical or compressed, acute 

 tubercle fitting into a pit in the upper jaw. 



The species will include M. australis, Tilesius, M. americanus, 

 Desm., M. latirostris, Harlan, M.fluviatilis, Illiger. 



The ribs of the African M. senegalensis are slender and com- 

 pressed; the sternal end is thicker and much narrower than 

 the middle part of the rib, but rather compressed and higher 

 than thick. In the American M. americanus the ribs are very 

 thick, solid, and heavy, compressed and broad in the middle, 

 and nearly cylindrical at the sternal end. 



The characters above given are the result of a generalized 

 description of the skulls from each country, rather than a rigid 

 individual description of any of them. 



The nasal bones are absent in all the African skulls, and 

 there is no appearance of any notch in the front edge of the 

 frontal bone, or groove in the upper margin of that bone on the 

 edge of the nasal opening ; so that if there is a nasal bone in 

 the flesh, it must be free from the other bones. 



The nasal bone is absent also in M. de Blainville's figure of 

 the skull from Senegal, in the Paris Museum. 



On the other hand, there is a distinct nasal bone, or a notch 

 in the outer edge of the first of the frontals, and a groove for its 

 reception, in all the skulls from America in the British Museum; 

 but the size of the bone appears to vary greatly in these speci- 

 mens. 



It is present, on one side, in the figure of the skull named 

 M. latirostris, from Cayenne, in M. de Blainville's ' Osteo- 

 graphie,' and in Dr. Harlan's figure of M. latirostris from Flo- 

 rida. Dr. Kraus states that the size and form of the nasal bone 

 were very variable in the specimens of Manatees that he re- 

 ceived from one locality (Surinam) ; and they are not present in 

 the skulls of M. australis and M. latirostris in the Paris Museum, 

 if we are to depend on M. de Blainville's figures ; nor are the 

 notches or grooves to be seen in these figures, and they are ab- 

 sent in the skull of the skeleton from Cuba in the College of 

 Surgeons. 



In the skulls of the African Manatee in the British Museum 

 and in M. de Blainville's figure of the skull at Paris, from Sene- 

 gal, the hinder or upper margin of the nasal aperture is con- 

 tracted, and the front edge of the frontal bone is thick and 

 rounded. The width of the arch of the upper edge of the nasal 

 aperture varies in these species ; in one it is narrow and ovate, 

 in another broader, and in the third much broader and nearly 

 straight-edged. 



In all the skulls from America the front edge of the frontal 

 bone is truncated, with a more or less thin, straight edge, which 



