392 PROCEEDINGS OF THE NATIONAL MUSEUM. vol.49 



case in Eoiherium^ they are pm* and pm^ or pm® and pm^ Since 

 Desmostylus is so primitive in other respects, the writer prefers to 

 regard them as pm^ and pm^ 



In the skull from Oregon there is present the base of a tooth 

 which belongs to the hinder premolar (pi. 57, !21). It is nearly cir- 

 cular in section, with a transverse diameter of 17 mm. and a longi- 

 tudinal diameter slightly less. There appears to be no reason for 

 supposmg that it had more than a single root, except that the Japan- 

 ese wi'iters say that the teeth m their specimen were two-rooted 

 in all cases. How many columns there were in this tooth it is impos- 

 sible to say with certainty; but the appearances are that there 

 were a large one on the inner side, a second large one m front and 

 nearer the outer side, and two smaller ones on the outer side and 

 toward the rear. This could not be greatly different from the tooth 

 regarded by the Japanese authors as pm^. 



With the skull here described there was sent a tooth which prob- 

 ably belonged to another individual (pi. 58, figs. 5, 6). It is com- 

 posed of four columns of equal size and these had undergone consid- 

 erable wear. The diameter of the tooth is 20 mm. This tooth has 

 a worn surface on a side of one of its columns where it had been in 

 contact with another tooth. This was certainly on the hinder face 

 of the tooth; and fron:j the form of the tooth I conclude that it 

 belonged on the left side, in case it was an upper tooth. It was 

 probably the hindermost premolar. 



Irmnediately in front of the hinder premolar is a socket for another 

 premolar; as I suppose, for pm^. This socket is 14 mm. long and 

 9 mm. wide. There is a corresponding one on the left side. Yoshi- 

 wara and Iwasaki found evidence in the wear of a lower tooth that 

 there was a premolar in front of the upper one which they described. 

 Just in front of the socket mentioned there is a little pit, about 

 3.5 mm. in diameter, from which a small tooth may have fallen be- 

 fore the death of this animal. Between this pit and the object which 

 is supposed to be a canine there is no evidence of the presence of other 

 teeth. For a distance of about 12 mm. in front of the pit mentioned 

 the narrow alveolar border is uninjured, but the remainder has the 

 border broken off. 



Behind the supposed pm^ there is the first molar (pi. 57, 2S). On 

 the left side of the skull this is broken off close to the bone and even 

 this is eroded ; on the right side aU the columns are broken off not far 

 from their common base. As preserved, the length of the crown is 

 40 mm. and the width 28 mm.; but by measuring nearer the bone 

 the length is only 35 mm.; the width 25 mm. The length and the 

 width of the complete tooth must have exceeded these figm'es some- 



' Andrews, Catalogue of the Tertiary Vertebrata of the Fayum, Egpyt, p. 208. 



