128 Annals of the Carnegie Museum. 



tral to the tapirs, but that it is closer to the Rhinoceroses. Again 

 referring to /. c. Pla e XLIV, Fig. 3, it is quite clear that the premolars 

 have unmistakably advanced towards such Ol'igocene genera as 

 Leptaceratherium trigonodum, Ccvnopus mile, or C. platycephalum. 

 This implies a very early origin of the "atypical" premolar structure, 

 to which Professor Osborn calls attention in his work on the Rhi- 

 noceroses referred to above. Nor is there any apparent reason for 

 excluding Ilyrachyus agrarius or Colonoceras agrestis as- also possibly 

 belonging to the Rhinoceroses, the latter genus to Diceratherium as 

 Marsh originally suggested."^ The Rhinocerotidce had, in the Uinta, 

 the Bridger, or even earlier Tertiary time, most likely made more than 

 the initial start towards their varied specilizations seen in later time. 

 I am inclined to the opinion, that, if we had found in America the true 

 middle Eocene ancestry of the various types of Rhinoceroses, in the 

 later epochs we would have met with even further advancements than 

 are recorded in the Bridger or later Eocene."'* The Amynodonts of 

 the Uinta are certainally surprisingly advanced along their line. 

 When the dentition of Desmatotherium is compared with that of 

 Isectolophus and Parisectolophus and the earlier genus Homogalax the 

 tendency toward the vertical increase of the crowns, or greater de- 

 velopment of the cement is clearly observed in Desmatotherium. 

 Besides the early origin of the tetartocone of P-, the cross-crests are 

 visibly of greater prominence and the valleys deeper than in the teeth 

 of Parisectolophus or even the Uinta genus Isectolophus. Altogether 

 the teeth, especially the molars, are more nearly like those in Hyra- 

 chyus, Colonoceras, or Hclaletes. In Ilyrachyus there is, however, 

 present a crista which is only faintly or not at all indicated in Des- 

 matotherium. In Colonoceras the crista is slightly better developed 

 than in Desmatotherium and the posterior cross-crests of the superior 

 premolars are also located further foward in Colo?ioceras.^^* Scott's 

 genus Desmatotherium should be placed with Ilyrachyus in a line 

 nearer to the Rhinocerotidce. It certainly appears to be more closely 

 related to that group that to the Tapiroidea, where it has been 

 heretofore placed. 



"- Amcr. Jour. Sci. (3), Vol. XIV, 1877, p. 362. 



"^ Europe during this time was nearer, or perhaps more accessible, to the center 

 of dispersion of the true Rhinoceroses, according to the works of Schlosser, Abel, 

 and others. 



"'' If these features in Colonoceras are constant they may be regarded as of con- 

 siderable importance. 



