48 DINOCERATA. 



The last upper premolar is very similar to the one just described. 

 Its crown is somewhat more triangular in outline, and the crests of the 

 transverse ridges are straighter. The basal ridge is continued and well 

 developed. 



The Uppek Molars. 



The first ti-ue molar is much like the last premolar in general form. 

 It shows by its greater wear that it made its appearance before the last 

 premolar, and in this way its true position in the series is indicated. The 

 anterior transverse crest in this tooth is considerably larger than the 

 posterior crest, and the valley between them is much Avider than in the 

 premolars. Behind tlie posterior crest, moreover, there is, on tlie iiuier 

 posterior angle of the crown, a distinct tubercle. This is seen in all of the 

 true molars in JJinocenis, and will distinguish them, at once, from pre- 

 molars of similar general form. Tlie basal ridge of this first molar is well 

 developed, except on the outer side, opposite the outlet of the transverse 

 valley. 



The second, or penultimate, upper molar is much larger than the first, 

 but similar in general form. The ti'ansverse and antero-posterior 

 diameters of the crown are nearly equal, tlie former being somewhat 

 greater. The basal ridge is well developed on the posterior side of the 

 crown, and distinct on tlie internal and anterior faces, Ijut is obsolete on 

 the external face, near the middle. 



Tlie last up[)er molar is much tlie largest of the series, and the 

 transverse diameter of the crown is considerably greater than the 

 antero-posterior diameter. The anterior crest is larger than the posterior, 

 and considerably curved, with the convexity in front. The posterior crest 

 is nearly straight, but does not join the anterior crest closely at its inner 

 extremity, the two forming a U-sliaped figure. Back of the crest, on the 

 posterior, internal border, there are two distinct tubercles in this specimen, 

 as shown in Plate VII, figure 2. The basal ridge is continuous, except 

 between the outer margin of the lateral crests, where it is lost in the 

 depression on this part of the crown. 



