46 DINOCERATA. 



In Tinoceras, the upper canines are much more curved than in- 

 Dinoceras, and the end of the root, instead of being- inserted in the 

 base of tlie maxillary horn-corej starts well back of it, so that the 

 general direction of this elevation is nearly at right angles to the tusk. 



The general form of the upper canine tusks in the Dinocerata is 

 shown in figures 49-52, on pages 44 and 45. 



In the lower jaw of Dinocera^, the canine is very small, and very 

 similar in form to the incisors, which it adjoins (Plate VIII, figure 1, c). 

 The same is true in the genus Tinoceras, where the lower canine, as well 

 as the incisors, has a more erect position than in Dlnoceras. 



The Upper Premolars. 



The crowns of the premolar and molai- teetli in iJiiioccrav, and, in 

 ffict, in all of the known JJii/oceruta, are remarkably short, witli the roots 

 well developed, forming a true brachyodout dentition, as in all early 

 Tertiary ungulates. These teeth are all inserted b>' thi-ee roots, two small 

 ones on the outer side, and a larger one on the inner side. 



In the type of Dhivrcrds iiiirdhile (number 10."!6), the up[)er molar 

 series is renuirkably well ju'eserved. The entire set of premolars and 

 molars is in position, indicating that the animal was fully adult, and yet 

 the amount of wear sliown by these teeth is so slight as not to obscure in 

 the least their essential characters. 



The form and relative position of the series on tlie two sides is Avell 

 shown in Plate VII, figure 2. There are three premolars, and three true 

 molars on each side, forming together a close series. There is, in this 

 skull, no trace of w hat may be regarded as the first j)remolar. If present 

 during the immature condition of the animal, it has entirely disappeared. 

 In one specimen of this genus (number 1039), the alveole of this first 

 upjier premolar remains, but no other trace of the tooth has been seen. 



The first premolar of THi/orrras miniJulr in jdace, which would 

 correspond to the second in the complete ungulate dentition, is tli<B 



