PERISSODACTYLA. 633 



meter of one of the roots of that tooth, and much less than that anterior to 

 it. The third and fourth premolars have the anterior external basal tubercle 

 well developed, besides the two external cusps of the crown. The latter are 

 subequally developed on the third premolar. The external faces of tlie 

 molars have only the vertical ridge at the middle of each lobe, but on the true 

 molars, while the anterior one retains its strength, it becomes obsolete on 

 the second and third teeth. The result is that these cusps have, on wearing, 

 a much more crescentic section than on species like H. venticoliim and R. 

 angustidens, where the external convexity remains. There are the merest 

 traces of external cingula on the molars to represent the strong ledges of 

 the other species mentioned. On the other hand, the cingula of the inner 

 bases of the crowns are strong, excepting opposite the posterior inner tuber- 

 cle, where they are wanting. Anterior and posterior cingula pi-esent. Tha 

 inner lobes of the crowns of the third and fourth premolars are rather wide 

 anteroposteriorly, and the valley between the internal tubercle and the 

 external wall is uninterrupted. It is bounded anteriorly by a ridge con- 

 necting the points mentioned, which forms the anterior border of the crown, 

 the anterior cingulum being absent or rudimental. There is a rudiment of 

 the posterior median tubercle on the fourth premolar. Both intermediate 

 tubei-cles are present on the true molars, the posterior forming a continuous^ 

 ridge with the posterior inner tubercle, while the anterior is more distinct 

 and is rather triangular in section. It sends a horn to the anterior angle 

 of the anterior external cusp, which is quite distinct from the anterior basal 

 cingulum and its cusp. The external face of the crown is wrinkled ; the 



internal is smooth. 



Measurements. 



M. 



Length of superior molar series 0565^ 



Length of superior premolars 0300 



Length of base of first premolar 0066 



Length of base of second premolar 0078 



Width of base of second premolar 0050 



Length of base of third premolar 0072 



Width of base of third premolar 0080 



Diameters base first true molar ^^°t*'^°P°«t^^"'^ ^ ""^^-^ 



( transverse viw 



Diameters base third true molar 5 P 



( transverse Olua 



Length from last molar to and including occipital condyle 0600 



Width between inner borders of postglenoid processes 0:i60 



Width of basioccipital bone opposite posttympanic processes 013(X 



