PROCEEDINGS OF THE NATIONAL MUSEUM. 



VOL. 65. 



been a progressive reduction of the replacement teeth. In Halithe- 

 rium the hindermost preniohir was not developed, and the corre- 

 sponding milk tooth assumed the form of a molar. 



We may then regard it as possible that the tooth 22 of my plate 

 67 is a milk tooth which was assuming the form of a molar, and which 

 was not to be displaced by a premolar, but by the first molar. The 

 tooth in front of it is then the third premolar, or the corresponding 

 milk molar. A deep pit in front of it represents the second pre- 

 molar or milk molar, and a minute pit in front of that represents the 

 first juvenile tooth. 



As to the tooth on which I based the genus CornwalUus it is then 

 possible that it is the liindermost milk tooth of Desmostylus; but this 

 is for the future to determine. I proceed to give a description of it : 

 The tooth (pis. 1, 2, figs. 4, 5) has suffered some loss of enamel on 

 two columns, as shown by the figures. All of the columns have 

 suffered some wear, but that they were of small height originally is 



evident. In two of them the wear had 

 not reached the core of dentine. The 

 columns taper rapidly from the base 

 to the summit. Text figure 1 presents 

 a view of this tooth before a fragment 

 of the second inner colunm had been 

 cemented in its place. It shows that 

 the dentine core, broad at its base, 

 tapers rapidly to its summit, as was 

 necessary in a low-croAvned tooth. As 

 seen from the figures, there are in front two large columns, and be- 

 hind these two somewhat smaller ones. At the rear is a column of 

 which a part is gone. It appears quite certain that the snag of 

 enamel at the right of the gap (pi. 1, fig. 4) formed part of a cusp 

 which adhered to the hinder column. Whether it could be counted 

 as the sixth column is doubtful. The tooth is taken to belong in 

 the right maxilla. 



The length, measured in the axis of the tooth, is 45 mm. ; the total 

 length 48.5 mm. ; the greatest thickness, 34 mm. ; the height of the 

 crown in front, 23 mm. On the front end there is a cingulum which 

 does not occupy the whole width of the tooth. At the inner end of 

 this are two small cusps., llootward from the edge of this cingulum 

 there is a surface 10 mm. long and 4 mm. deep, which is worn from 

 contact with a tooth in front. Between the cingulum and the grind- 

 ing surface there is on each of the two anterior columns an extensive 

 worn surface. No such surface is seen on the hinder end of the 

 tooth. The cingidum is not developed on the sides and rear of the 

 tootli; but at the outer end of the first transverse valley there is a 

 large tubercle, worn at the summit and showing a pit of dentine. At 



Fig. 1.- — Tooth of Cohnwallius 

 sooKENSis. View from inner 

 SIDE. Type. 



