TRANSACTIONS OF WAGNER 

 SO 



UINTA SELENODONTS 



like those of Poebrotlicrinvi and of nearly the same relative length ; they 

 extend, however, much farther back than in the White River genus, reaching 

 nearly to the middle of the orbit, while in the latter the fronto-nasal suture is 

 some distance in advance of the orbit. This posterior extension, in Protylopus, 

 compensates for the elongation of the anterior part of the muzzle which char- 

 acterizes Poebrotherium. Another difference between the two genera may be 

 seen in the shape of the free ends of the nasals, which in the Uinta type are 

 bluntly pointed and extend beyond the edges of the preniaxillaries, and in the 

 White River form they are emarginated into a semicircular notch, of which 

 the lateral edges extend farthest forward, but not beyond the premaxillse. In 

 short, in Poebroihermm the frontals have been elongated, pushing the nasals 

 before them, as it were; at the same time, the whole anterior part of the face 

 has grown longer, so that, in spite of their less extension backward, the nasals 

 are relatively as long as before. 



The maxillary is much the largest bone of the face, of which it forms 

 the greater portion ; it is very long, but of only moderate vertical height, 

 which, except in the orbital region, is nearly uniform throughout its length. 

 In correspondence with the very brachyodont character of the teeth, the 

 alveolar portion of the maxillary is very low. The masseteric ridge and sur- 

 face are carried over for a short distance upon the maxillary. The anterior 

 border, formed by the premaxillary suture, is nearly vertical, but inclines 

 backward a little at the upper end. In addition to the vacuity or fontanelle 

 already mentioned, there appears to be another, of narrow, slit-form, between 

 the maxillary and the nasal. Less uncertainty attaches to this opening, 

 though it also may possibly be due to dislocation. The infraorbital foramen 

 is small, narrow, and inconspicuous, and is widely removed from the orbit, 

 opening above p^'^, the same position that it occupies in Poebrotherium. From 

 the general shape of the skull it is plain that the palate was shaped much as 

 in the latter genus, quite broad behind and contracting very much in front, 

 where the whole muzzle becomes exceedingly slender. This contraction is 

 gradual, not abrupt, as it is in the recent Tylopoda. 



The premaxillary has a very broad ascending ramus, but in spite of this 

 extension upon the face, it has but a relatively short contact with the nasal, 

 because of the absence of any distinct nasal process. For the same reason, 

 the premaxillary is very widely removed from the frontal, of which the nasal 

 process is very short. The alveolar portion is short and low, and very nar- 

 row transversely, because the incisors are arranged in nearly the same fore- 



