Douglass : Merycochcerus. 95 



upper borders of the maxillaries and opening upward. Premaxillaries 

 united for a long distance and forming a spout-shaped depression which 

 is concave transversely and convex longitudinally. Sides office concave 

 below horizontal portion of posterior nares. Malar below orbit very 

 deep but squamosal portion of zygomatic arch light. Mandible heavy and 

 angle extremely large and deep. Both the mandible and sides of the face, 

 especially the malar portion, fitted for the attachment of heavy muscles. 

 Premolar series of teeth shoi'tened and crowded. Molar series increas- 

 ingly hypsodont. Incisors small. 



It will not be necessary to redescribe the skull, but I have made 

 comparisons with the types of Merycochcerus proprius, Merycochan'us ? 

 rusticus, and skulls of Merycochcerus collected by Mr. O. A. Peterson 

 in the Harrison or upper Monroe Creek beds in Nebraska. 



Comparison with Merycochcerus proprius. 

 In Pronomotherium laticeps the premaxillaries, as seen from in front, 

 are narrower and more concave, are trough-shaped, not simply having 

 a narrow median channel near the alveolar border as in Merycochcerus 

 proprius; the anterior palatine foramina are not so large; themalo- 

 maxillary ridge is more prominent, the face not so nearly flat, but is 

 much more deeply concave above the ridge just mentioned ; the infra- 

 orbital foramen is on the nearly horizontal shelf above this ridge 

 instead of opening on the nearly vertical portion of the face; the in- 

 cisive border is much narrower, so it is evident that the incisors were 

 smaller. The first premolar is oblique, and there is no space between 

 this and the second premolar. The space in front of Pi is much 

 shorter than in Merycochcerus proprius. There are but faint traces of 

 cingula on the teeth posterior to P-i, while in the type of Merycochoerus 

 proprius they are strong and heavy. The teeth are all narrower, P-2- 

 is shorter and P^ has not the peculiar pattern of the type of Meryco- 

 chcerus proprius as it apparently had only two pits. P^ is of the 

 same length but is narrower, giving it a quite different appearance. 

 This is also true of Mi. The second and third premolars are not such 

 broad and heavy teeth, and the ridges and buttresses are not so heavy. 

 The posterior outer lobe of M^ is much narrower and is directed out- 

 ward, not extending much behind the posterior horn of the posterior 

 inner crescent ; the posterior half of the tooth is much narrower, and 

 there are no median ridges on the outer surfaces of the outer crescents 

 in the molars. 



