148 SPECIMENS OF SIRENIA. 



tuberculated crown. In No. 3 were three pairs of 

 molar teeth, of which the posterior, ^ inch in sagittal 

 and ^ inch in transverse diameter, was the largest. 

 In No. 2 five pairs of sockets were present, in which 

 only two teeth had been preserved. In No. 1 only 

 three sockets were on each side ; the tooth in the 

 middle socket measured 1^ hy | inch; the hindmost 

 tooth had been lost. 



In the Upper Jaw the premaxillary or incisor teeth 

 assumed in the older skulls the form of tusks. The 

 youngest skull, No. 4, had two sockets in each pre- 

 maxilla, separated by a transverse septum, each of 

 which contained an unerupted tooth ; the anterior was 

 styliform, and the posterior about three times thicker. 

 In No. 3 each premaxilla had only a single large 

 socket for a tusk, of which the left was preserved; 

 the socket was 4| inches deep, 1^ inch wide. In 

 No. 1 the tusk was present in each premaxilla; 

 it projected 2| inches, and its circumference at the 

 mouth of the socket was Sk inches. In No. 4 the 

 maxillary or molar teeth had six sockets on each side ; 

 in the most anterior the tooth was cylindriform and 

 only I inch in diameter ; the 2nd, 3rd, and 4th were 

 flattened on the crown ; the 5th had recently erupted 

 and was tuberculated, the 6tli was concealed in the 

 socket. In No. 3 were three pairs of sockets, and the 

 posterior on one side contained a worn tooth | by 

 1 inch in diameter. In No. 2 were five sockets on 

 each side, but only three teeth with worn crowns had 

 been preserved. In the oldest skull, No. 1, were only 

 two sockets and two pairs of teeth. 



From these observations it would appear that in 

 early life two incisor teeth arise in each premaxilla, but 

 that one disappears, whilst the other increases greatly 

 in size and forms the tusk. At the stage in which 

 the four incisors were seen in the youngest skull, the 

 more posterior in each bone was the larger, from 

 which it would seem as if it developed into the tusk 

 and caused the absorption of the anterior tooth. As 

 i-egards the molar teeth, six is the number developed 

 on each side, but they are not all erupted at the same 

 time, for when the 1st is in place the 6th is still 

 concealed, and before it appears the 1st and perhaps 

 the 2nd may be shed, so that in the course of time 

 four, three, or only two molars, and these the most 

 posterior, may be all that remain on each side. The 



