OF THE WHITE RIVER BEDS OF MONTANA. 



257 



The parts of the present specimens are small, being anterior fragments of mandi- 

 bles, yet- these parts are so perfectly characteristic in Merycochcerus (?) that I cannot avoid 

 the belief that if the skull of this animal is found it will show a strong leaning toward 

 that genus, and I would not be surprised if it proved to be the White Eiver ancestor. 

 This is made more probable by the fact that none of the Oreodontidce that have been 

 described can be considered as ancestral to Merycochcerus, either the true genus or the 

 doubtful one. I do not refer to the John Day forms, Promerycochmri, which have been 

 included in that genus. They are a very different animal. 



The specimens are (48) the anterior part of a right ramus of a mandible, with part 

 of the alveolus of the canine, the root of P T , the alveolus of P T and the last two premo- 

 lars complete, and (66) a part of a right ramus with the last three premolars and the 



first molar. 



There are four ways in which it differs from Merycoehoerm (?). It is only a frac- 

 tion of the size ; it has, like some species of Leptauchenia, two mental foramina ; the 

 premolar teeth are not crowded, and the teeth arc not so high. The premolar series was 

 probably as long as the molar series. 



In the form of the chin and symphysis, the depth of the jaw, the narrowness of the 

 space between the rami back of the symphysis, the evident reduction of the incisors, the 

 smallncss of the canine, the lenticular section of P T , the forms of all the teeth preserved, 

 their narrowness in proportion to their length, are all like Merycochwrm (?). It may be 

 that these two fragments belong to different species, so to save confusion I will describe 



them separately. 



Specimen 48.— The anterior upper tip of the ramus is broken off. This shows ante- 

 riorly a, transversely narrow broken surface, nearly in the middle of which is the canine 

 alveolus, but no hint of incisors. It is very doubtful if there was the full number. If 

 there was they must have been exceedingly small or placed anteriorly to the canine. 

 The anterior surface of the chin as far as shown is steep and straight along the sym- 

 physeal suture. It is convex transversely. The anterior mental foramen is beneath the 

 posterior part of P ;! , the posterior one a little behind the middle of 1\. They are a 

 little above the longitudinal middle line of the ramus. The anterior is the larger. 'Hie 

 symphyseal suture, is broadest below and narrows upward as in Merycochwrm (?). The 

 posterior of the symphysis is under the anterior part of P T . 



The canine was evidently much smaller than P T . P r is lenticular in section with 

 nearly equal sides and rounded angles, the longest diameter being obliquely fore-and-aft, 

 and directed posteriorly outward and anteriorly inward as in Merycochcerus (?). I\ had 

 two roots near together. P ;T has a proportionally large paraconid, which as the tooth is 

 viewed from the outside is seen to be separated above by a distinct notch from the pro- 



