74 THE MERYCQIDODONTID/F. 



Foramina: The infraorbitals are above the posterior part of P 3 . The supraorbitals are 

 21 mm. apart. 



Dentition: The length of the superior dental series is intermediate between that of E. pacificus 

 and of E. leptacanthus. The superior molar-premolar index is 1.00, and that of the inferior series 

 is 0.93. 



Discussion: Cat. Nos. 11011 and 12320 Y.P.M. are probably males, while Cat. No. 12319 

 Y.P.M. is more delicately proportioned and may well be a female. In the last the nasal bones and 

 the face are much narrower, the orbits smaller, and the whole skull and jaws less robust than in the 

 other two. 



Eporeodon major (Leidy) 1854 

 Fig. 7 ; PI. VI, figs. 1-3 



Original Reference: The ancient fauna of Nebraska. Smithson. Contribs. to Knowledge, VI, Art. 

 VII, p. 55, pi. IV, fig. 6 (Oreodon -major, synonym Merycoldodon major). 



Type Locality: White River, South Dakota. Referred material from Wyoming, Nebraska, and Oregon. 



Geologic Horizon: Upper Oligocene (upper Brule). 



Types: Holotype, right maxillary with molar series, collected by Dr. Owen about 1853. Allotype, Cat. No. 

 10863 A.N.S.P., a remarkably well-preserved skull. 



Specific Characters: The skull is about the length of that of E. leptacanthus and is larger 

 than that of Merycoidodon culbertsonii. It is nearly flat in superior profile and is mesocephalic. 

 The maximum expansion of the zygomata is just in advance of the glenoid surface. The zygomata 

 are moderately heavy and curve upward to the front of the glenoid and then downward posteriorly. 

 The squamosal portion is deeper than the malar. The nasal bones are posteriorly acute, broad and 

 of nearly uniform width, and transversely convex. The pars facialis is relatively small, and the 

 lacrimal fossa is small and rather shallow but well defined. The frontals are wide and transversely 

 convex, extending forward of the lacrimal, and are not depressed along the sagittal plane, except 

 near the frontoparietal suture. The orbits are proportionately small — absolutely no larger than 

 those of M. culbertsonii — and somewhat vertically oval. The temporal ridges unite just above the 

 anterior edge of the glenoid surface. The sagittal crest is moderately high and about a third of the 

 skull length. The supraoccipital crest is posteriorly much produced, and the wings are widespread. 

 The brain case is proportionally narrow, with a prominent parietosquamosal convexity. The external 

 auditory meatus is in the main outwardly directed. The palate is wide and nearly flat, and the 

 U-shaped palatonarial border is produced well beyond the molars. The basicranial axis is moder- 

 ately bent on the facial axis. The glenoid articular surface is large and concave. The postglenoid 

 process is large and externally oblique, bounds more than half of the articular surface, and is in 

 contact with the bulla. 



Leidy (1869, p. 100) described the very large bulla "as a crescentoid convex prominence, 

 curving from within the position of the postglenoid tubercle to the root of the para-mastoid process." 



His description continues: 



A ridge-like prolongation, forming the posterior horn of the crescent, abuts upon the latter process. A 

 second ridge is directed outwardly backward and upward, forming the other horn of the crescent, and corresponds 

 with the vaginal process of the human temporal. From the fore part of the bulla a short process projects exterior 

 to the eustachian orifice. Between the convex inner surface of the bulla and the basi-occipital and basi-sphenoid 

 there exists a wide reniform fissure, at the bottom of which the periotic bone is visible. The external concave 

 surface of the bulla includes the space occupied by the styloid bone. 



The paroccipital process is triangular in section, is directed forward, outward, and downward, 

 and is closely appressed to the bulla. Index: 0.56. 



Foramina: The infraorbitals lie above the anterior half of P 3 . The supraorbitals are 14 mm. 

 apart. The posterior palatine foramina are nearly on a line with the interval between P 3 and P 4 . 



