Peterson : A New Titanothere from the Uinta Eocene. 31 



portion abruptly turned downwards and convex on the anterior border; 

 incisors well in front of the canines and relatively subequal in size; 

 canines proportionally small. 



Skull. 

 Plates VI-VIII. 

 In comparing the recently discovered material with the best pre- 

 served remains of Protitanotherinm (P. emarginatum Hatcher) a 

 number of important differences are at once observed. The nasals 

 of the new species are longer, thinner, somewhat narrower (especially 

 in specimen No. 2859); furthermore the lateral borders of the nasals 

 are much less thickened, and instead of the broadly emarginated area 

 at the free end of the nasals in P. emarginatum, the termination of the 

 nasal of the present form has an abrupt downward turn, resembling 

 that of Megacerops coloradensis Leidy, and its anterior margin is very 

 convex transversely, instead of concave, as is the case in P. emargina- 

 tum. Upon the whole the nasals of the species we are describing 

 extend further forward. There seems to be a considerable variation 

 in the development of the horn-cores; thus, in skull No. 2858 this 

 protuberance appears to have a development comparable to that of 

 some of the titanotheres found in the Oligocene, while in specimen 

 No. 2859 these osseous bosses aie very much smaller, more conical, 

 and in proportion more like those of P. emarginatum, in spite of the 

 fact that the skull we are considering pertains to an old individual 

 (see PI. VII). This varied development of the horn-cores is no 

 doubt due to sexual differences, or possibly to individual vaiiation. 

 The premaxillaiies extend well in front of the maxillaries, and are 

 separated in front, forming a deep median notch, as in P. emarginatum, 

 so that the median pair of incisors are wide apart, while fuither back 

 they are firmly coossified and also solidly fused with the maxillaiies. 

 The infraorbital foramen is also of large size as in P. emarginatum 

 and located above P- as in the latter species. The maxillary is on 

 the whole very robust, and shows that it had advanced well towards 

 the condition found in Diplacodon and Titanotherium. This is also 

 true of the jugal, the prominent lower border of which has the down- 

 ward and backward sweep in front of and under the orbit, which is 

 characteristic of Titanotherium. The zygomatic arch, though widely 

 expanded behind, is, however, less robust than in the Oligocene genus, 

 and agiees better with the type of Diplacodon elatum described by 



