400 THE MAMMALIA OF THE UINTA FOKMATION. 



inflation occurs botli in Agriochoerns and in the oldest species of Oreodon which are 

 found in the lowest horizon of the White River formation, the Tttanotherium beds. 



The maxillary resembles that of Oreodon, being very low beneath the orbit and 

 extending up to the nasals in advance of the lachrymal ; the alveolar portion is low 

 throughout in correspondence with the exceedingly low crowns of the teeth, and even 

 the portion of the maxillary which forms the side wall of the nasal cavity is propor- 

 tionately lower than in the Miocene genus. The palatine processes are rather narrow, 

 and a narrow incision occurs between the alveolus of the last molar and the palatine 

 l^late; this incision is also present in Oreodon, but is broader. The infraorbital fora- 

 men is situated above the penultimate (pm. 3), which is the position it occupies in 

 Agriochcerus, while in Oreodon it is placed somewhat more anteriorly. I^^either 

 nasals nor premaxillaries ai-e preseiwed in any of the specimens. 



The mandible is short and deep, with an abruptly rounded chin and long, very 

 steeply placed symphysis. The condyle is shaped very much as in Oreodon, but the 

 coronoid process is more like that of Agriochoerus in being higher and more deeply 

 sepai'ated from the condyle, and consequently less like that of the peccar3^ So far 

 as can be determined the angle of the mandible was not so much thickened as in 

 Oreodon; the two rami are not closely interlocked and even in old individuals show 

 no tendency to coossification. 



The dentition is of especial intei;est as it serves to connect the isolated and pecu- 

 liar family of the Oreodontidce with the other selenodonts of the American and Euro- 

 pean Eocene. 



Upjjer jaw. The superior incisors are not repi-esented in the collection, and only 

 the fang of the superior canine; the latter, however, shows the characteristic D- 

 shaped section seen in Oreodon, and doubtless the crown presented no important 

 ditlerences. The same statement applies to the most anterior pi-emolar (pm. 1). 

 The second premolar, seen from the outer side, resembles much the coi'respond- 

 ing tooth in Oreodon,, having a compi'essed conical crown with trenchant edges. 

 Seen from below, however, it is more simply constructed, as the small internal access- 

 oi-y valleys are barely indicated, and the cingulum is but feebly developed. The 

 third premolar is moi-e transversely extended than the preceding one and has the ex- 

 ternal wall slightly concave, but is constructed essentially like it, and is consequently 

 simpler than the same tooth in Oreodon. Loidy describes these premolars in Oreodon 

 as follows (]S[o. 7, p. 81) : "The anterior thi-ee upper premolars are constructed after 

 the same plan. They decrease successively in size and in the degree of develop- 

 ment of theii- details of form, fi'om the third to the ftrst of the series. Theii- 

 crown is a trilateral [)yramid, with a pointed apex and a broad external cordiform 



