THE TEETH. 



47 



smallest of the present series. Its crown is subtriangular in outline, with 

 the apex in front. The antero-exterual face is cordate in outline, 

 somewhat concave, with the point below. On the inner side, there is 

 an elev^ated lobe, somewhat inside of, and separated from, the apex of the 

 external face. On tlie inner and posterior faces of this premolar, there 

 is a strong basal ridge, which is nearly or quite obsolete on the anterioi' 

 face. 



Figure 53. — Upper molar .series of Tinoceras stenops. Marsh (No. 1567); seen frum below. 

 Figure 54. — Lower molar series of same specimen ; seen from above, m. molar ; pm. preaiolar. 



The figures axe three-fourths natural size. 



The second upper premolar in this series is much larger than the 

 one last described. The crown is sub-cordate in outline, the apex pointing 

 inward, and somewhat backward. The essential features of the crown 

 consist of two transverse ridges, which meet internally, forming a 

 V-shaped figure. This is the characteristic type of the upper niolai- 

 series in the Dinocerata. The anterior transverse ridge of this tooth lias 

 its external extremity somewhat curved backward. This premolar has a 

 well marked baSal ridge, entirely surrounding it, although somewhat thin 

 near the middle of the anterior border. 



