THE LOWER EMBAR OF WYOMING 651 



Associated with the other specimens are forms of the following 

 description that belong with the lower teeth. The teeth are long, 

 slender, and narrow gradually toward the strongly arched inner end. 

 The inner end forms a 35 arc of a circle 11 cm. in diameter; the 

 outer end forms a 90 arc of a circle 35 mm. in diameter. The 

 tooth is thick along the hinder margin to near the outer end, 

 and thin along the front margin to near the outer end, where it 

 sometimes becomes knifelike. A high, rounded ridge with a narrow 

 top forms the greater part of the tooth. From the top of the ridge 

 the surface slopes steeply to the back margin and almost as steeply 

 toward the front, where the slope becomes gentle and the edge is 

 slightly upturned. The surface is marked by undulations of the 

 same type as on the maxillary teeth, but these are often indistinct. 

 The surface punctation is fine. Only a few of the teeth show strong 

 wear, and this is at the top of the arch and toward the front end. 



These teeth were compared with the fragment described by 

 St. John and Worthen and agree with it in every way, except that 

 they are more massive. 



The most striking peculiarity of Deltodus mercurii is the strong, 

 subequally spaced, transverse undulations, but in many specimens 

 these are inconspicuous or absent. 



Trautschold 1 figures and describes . as Poecilodus grandis part 

 of a tooth that probably belongs to Deltodus mercurii. 



The restoration. — The Deltodus mercurii teeth from the Embar 

 all come from the same horizon, and there appears to be no 

 other species of Deltodus associated with them. They thus afford 

 a chance for determining their arrangement in the jaws. The 

 teeth figured in PI. V, Figs. 3 and 5, were found in the matrix 

 within 6 inches of each other, and they fit perfectly as upper and 

 lower dental plates. As shown in PI. V, Figs. 2 and 4, the mandib- 

 ular teeth are much more strongly curved than the maxillary, 

 and the narrow teeth described above fit against them as shown in 

 PL III, Figs. 1 and 3. By working a mandibular tooth against 

 modeling clay a depression of the same kind as shown in the teeth 

 figured is formed in the clay. 



The maxillary tooth is not adapted to fit against any other 

 teeth, and no teeth that seem to belong in the same jaw were 



1 Nonv. Mem. Soc. Imp. Natur. Moscou., XIV, 149-50, PI. XVII, Figs. 13a and b. 



