2 PROCEEDINGS OF THE NATIONAL MUSEUM. vol. 65. 



covered with a thin coat of cement. On the inner face of the tooth 

 there still adheres a part of the maxiliary bone. So far as the 

 writer sees, it is impossible to determine where in the molar series 

 this tooth belongs. No surface shows contact with a tooth in front 

 or behind. 



The determination of the dentition of Desmosfi/Iiis is a matter 

 of great interest. An examination of Yoshiwara and Iwasakrs 

 figures' shows that there is, in front of their first molar, a small 

 tooth consisting of only four columns. In the skull from Oregon, 

 which the writer described in lOla,^ there is in front of a molar 

 (pi. 57, 23) apparently corresponding to that figured by the Japanese 

 authors, and composed of the same number of columns, 8, the base 

 of a smaller tooth which was regarded 'as the first molar (pi. 

 57, 22). This supposed first molar, instead of being made up of 

 eight columns, appears to have only five. The tooth in front of 

 this (pi. 57, 21) is represented by the base of the crown and the 

 root, and it has a diameter of 17 mm. On plate 58 of the paper 

 cited, was presented the figure of a tooth which had four columns 

 and which was believed to be the fourth premolar. This appears 

 to correspond to the hinder premolar described by Yoshiwara and 

 Iwasaki. Now, according to these identifications, the Oregon skull 

 differs from the one found in Japan in having between the sup- 

 posed last premolar with four columns and the molar with eight 

 columns another tooth possessing apparently only five columns. It 

 is improbable that the two species differed in such an important 

 respect. 



An examination of my figure ^ shows that the molar indicated by 

 23 was emerging behind and above the supposed first m.olar 22. 

 This tooth 22 can hardly be a premolar, for this might be expected 

 to appear only after the molar behind it had come into action. One 

 might insist also that it is not a milk tooth, because there appears 

 to be no premolar to replace it, as shown by Yoshiwara and Iwasaki's 

 figure. Plate 2 of the Japanese authors shows that another molar 

 (their M-) was moving downward and forward to take its place 

 against the molar then in action— that is, it appears that the upper 

 molars, on coming into place, move downward and forward as in 

 the mastodons and elephants. 



If, now, we grant that, as the supposed first molar (22) of the 

 Oregon specimen became worn down, the next molar (23) moved 

 forward, pushed it out, and took its place, the condition seen in 

 Yoshiwara and Iwasaki's specimen would be produced. According 

 to this interpretation, the hinder premolar of the paper last cited 



1 Journ. Coll. Sci., Japan, Imp. Univ., vol. 16, 1902, pi. 2 ; pi. 3, fig. 4. 

 zProc. U. S. Nat. Mus., vol. 49, p. 381, pi. ol. 

 » Idem. pi. \>7. 



I 



