Peterson: The Osteology of Promerycochcerus. 161 



canines and presents nearly a straight transverse line from side to 

 side between the canines. The alveolar border is rather weak and 

 does not furnish much support for the incisors; consequently the latter 

 are relatively small and peg-like. Posteriorly the premaxillaries 

 assume an almost vertical position against the anterior portion of the 

 maxillaries. The anterior nares are of moderately large size and their 

 lateral borders are vertical. Inferiorly there are large anterior palatine 

 foramina, separated by the bony rods of the palatine plates of the 

 premaxillaries. 



The zygomatic process of the jugal, though not as prominent as the 

 zygomatic process of the squamosal, is fully as characteristic. The 

 outline of the jugal may be regarded as sub-triangular with the most 

 truncated point in front; the shortest and sharpest point (postorbital 

 process) above and the longest point extending outward, backward, 

 and downward to meet the process of the squamosal. The area below 

 and in front of the orbit is quite smooth and is slightly concave, while 

 further back the external face is plane, having a great vertical diameter 

 opposite the postorbital process. The wing-like zygonmtic process 

 ends rather abruptly against the anterior portion of the heavy zygo- 

 matic process of the squamosal, forming a very prominent and well- 

 defined border for the posterior attachments of the facial muscles. 

 The lower border of the zygomatic process of the jugal is also quite 

 sharp. 



The lateral and posterior boundaries of the nasals cannot be de- 

 termined from the material at hand. This area presents a regularly 

 convex surface from side to side and a long shallow antero-posterior 

 concavity in the middle. Anteriorly the nasals are greatly produced; 

 they terminate in a rounded blunt point and are always inclined forward 

 and downward. 



THE mandible. 



The ramus in this species is characterized by a heavy horizontal 

 portion with a thick and rounded angle and a rather long ascending 

 portion with a short and stubby coronoid process. Anteriorly the 

 upper portion of the mandibles flares out in order to give support to 

 the very heavy caniniform Py and internally there is also a liberal 

 space on the alveolar border for the incisiform canine and the incisors. 

 The two rami form a broad surface across the symphysis and along 

 the alveolar border. The anterior portion of the alveolar border has a 

 sudden peculiar outward curvature, which is due to the outward 



