Douglass : New Merycoidodonts. 105 



humerus, portions of a scapula, a radius, an ulna, a pelvis and a tibia. 

 From the Canon Ferry Beds (Middle or upper Miocene) at Canon Ferry 

 on the Missouri River about twenty miles east of Helena, Montana. 

 The species is one of the largest of the family. The skull is of the 

 long and narrow type ; the face is long and narrow ; the upper line 

 of the skull is nearly straight ; the sagittal crest is quite high, but not 

 heavy ; the occiput overhanging ; the brain-case is comparatively small ; 

 the posterior portion of the occiput is pillar-like, with two deep lateral 

 concavities. The tympanic bullae, though inflated, are not large in pro- 

 portion to the size of the skull. The paroccipitals are high, their 

 longest diameter is in a postero-internal and antero-external direction, 

 and they lie posterior to the outer portion and external to the pos- 

 terior portions of the tympanic bullae against which they are closely 

 pressed, they also come near to the high post-glenoid processes. 

 The external auditory meatus is closely compressed between these 

 two processes and has a flattened wing which is suturally united with 

 the post-glenoid process on its posterior surface near its base. The 

 basi-cranial axis is steeply inclined. The posterior angle of the zygo- 

 matic arch is not heavy or high ; the anterior process of the squamosal 

 is comparatively slender, but the malar beneath the orbit is deep. 

 A broad convex ridge extends from the anterior portion of the arch 

 to the posterior upper portion of the anterior nares ; below this the 

 face is somewhat concave. The mandible is long and the chin convex. 

 One of the most peculiar characters of this animal is what appears to 

 be an enormous enlargement of the fossa, usually small, which occurs 

 on the anterior portion of the ascending ramus of the mandible above, 

 and posterior to the last molar tooth. This fossa is deep, as well as 

 large, and has for its posterior boundary a plate of bone separating it 

 from the masseteric fossa which it has almost crowded out of existence. 

 All the teeth are large, heavy, and closely crowded ; in fact I know 

 of no other member of the family with such strong dentition. The 

 teeth have some peculiarities which there is not space at present to 

 describe. The skeleton is not as robust as that of Promerycochcerus 

 holla?idi, although the skull is larger. 



Measurements. 



mm. 



Total length of skull 390 



Length of upper dental series 213 



Width of skull just anterior to glenoid articular surface 180 



Height of skull at posterior of 1VP 100 



