THE MAMMALIA OF THE UINTA FOKMATIOV. 501 



measurements agree fairly well with those of the so-called AgriocJioirus pumUiis 

 Marsh, with which this species may prove to be identical. 



Jleasuremetiis. }f. 



LoDglh upper mohir scries (entire) •; .05:5 



" " preiiioliir series ? .020 



" " true molar •' 027 



Length lower moliir series (entire) 054 



" " premolar series 027 



" " true molar " 027 



Third upper molar, anlero-posterior diameter 010 



" " " transverse " (lOS 



" lower " anteroposterior " 012 



" " " transverse " 000 



Although the teeth preserved in the Princeton collection all belong to P.jiarvus, 

 there are several limb and foot bones which exceed those of the type species so 

 greatly in size, that they very probably belong to a larger species. They differ, 

 however, only in size and must unquestionably be referred to the same genus. Size 

 alone is not a very satisfactory criterion, but it seems unlikely that such differences 

 can be within the limits of mere sexual or individual variation. The Ibllowing 

 measurements will show the size of these larger specimens of I'rotoreodou as com- 

 pared with that of Oreodon Culbertsoni. 



JUeaiurermnU. 



Protoreodon. 0. Culbertsoni. 

 Af. M. 



Breadth of humeral trochlea 016 .021 



Height " " •• (Ill .(ii;t 



Length of calcaneiim OoO .0)2 



Sysietnatic I^o.^ition and lielalionsliips of Protoreodon. 



Tt will be obvious from the foregoing description that Protorpodon is very closely 

 allied to the White Kiver genus Oreodon, and may safely be regarded as the ancestor of 

 that genus. This relationship is made clear b}' a comi)arison of the skull, the teeth and 

 the feet, where the differences which Protoreodon exhibits from its Miocene successor 

 are just these tendencies towards the simplification that we should naturally expect to 

 find in the ancestral type. More particularly the i)resencc of the liflh cusp in the 

 upi)er molai-s is a welcome indication of the connection between the oreodonfs and 

 the buno-selenodonts of the earlier Eocene. On the other liaiid. I'rotoreodon has 

 many points of resemblance to Aiiriodnvrus, which are somewhat as follows : (1) IMie 

 shape of the cranium and the remarkable clougalion of its posterior portion: (i!) the 



A. v. S. — VOL. XV'I. '6\.. 



