THE MAMMALIA OF THE UIXTA FORMATION". 49.'} 



an oblique ridge desoends internally and terminates in a huge trilateral pointed 

 tubercle which springs from the middle of the base of the crown and rises nearly as 

 high as the principal point." In Protoreodon this tooth has a very much smaller 

 transverse diameter than in the Miocene genus ; the anterior half of the crown is 

 much less concave on the inner side, and it would seem that the internal tubercle was 

 I'udimentary and the posterior valley small. At all events, the greater simplicity of 

 the tooth can be seen from the anterior half of the crown, which is uninjured. 



The true molars differ in several important respects from those of Oreodon and 

 are more like, but not identical with, those of Agrioclicerus. The inner crescents are 

 more conical and less compressed than in the former genus, and the outer cusps are 

 less distinctly crescent-shaped ; they are also more widely separated from the inner 

 crescents, so that the valleys are much broader and shallower. The anterior pair of 

 crescents is much more completely sepai'ated from the posterior than in Oreodon, by 

 a depression which runs across the crown. All this is equivalent to saying that in 

 Protoreodon the selenodont pattei-n of the lower molai's is much less completely de- 

 veloped than in Oreodon. Compared with the molars of Agrioclicerus, those of the 

 Uinta genus present the following dilt'erences : The internal crescents are convex on 

 the inner side, instead of being concave with a median ridge, and the basal tubercles 

 on these crescents are smaller ; the outei- crescents are less flattened and the bones 

 slightly more prominent, though leaving the valleys open in front. As in this genus, 

 the heel of the last molar is proportionately larger than in Oreodon. 



The hrain of Protoreodon (PI. Ill, Fig. 1''), as indicated by the shape and size 

 of the brain ease, is very narrow and considerably elongated ; the hemisphei'cs aie 

 especially small and more simply convoluted than in Oreodon ; the convolutions are, 

 as in this gonus. latiiL'r broad and have a nearly straight fore and aft direction, con- 

 verging in fi'ont ; the niedihiteral gyrus is not very distinctly mai'kcd. The posterior 

 region of the brain including the cerebellum and medulla is very long in proportion 

 to the hemispheres, and apparently the corpora qnadrn/eimna were partially uncov- 

 ered V)y the interspace separating the hemispheres from the cerebellum. As a whole, 

 the brain is distinctly smaller in jjroportion than in the Miocene genera of the group. 



The vertebral column is rejjresented in the collection by many s|)ecimcns fiom all 

 the regions; but as they are not in an especially good state of preservation, and as 

 they do not show any very striking dilVerenccs from the vcrlcbriv of Orrodmi. they 

 will not rer[uii-c an extended description. 



The atlas is very similar to that of Or'odon and lescnibles tlKrrrur.' that of the 

 tragulines rather than that of the Pecora ; it is short in the antero-posterior direction, 



A. I'. S.— Vf)I,. \\[. 3k. 



