PROMERYCOCHCERUS 135 



genus, nor is this brought about by the spreading of the bones mentioned above. The very wide 

 palate is flat anteriorly and vaulted aft, with the U-shaped palatonarial border nearly beneath the 

 postorbital constriction. The shallowly convex glenoid articular surface is somewhat more than two 

 and a half times as long transversely as it is anteroposteriorly. The postglenoid process is relatively 

 small but stocky, with the two diameters nearly equal. The bulla; are large and suboval, and they 

 extend slightly below the level of the postglenoid process. The large paroccipital process is triangu- 

 lar in section and is not in contact with the bulla. There is a wide interval between the paroccipital 

 and postglenoid processes. Index: 0.635. 



Foramina: The infraorbital foramina lie above the interval between P 4 and M 1 . The supra- 

 orbitals are 16 mm. apart. The posterior palatine foramina cannot be seen. 



Dentition: There is an exceedingly heavy metastyle on M 3 , and the molars, together with P 4 , 

 have internal cingula. The superior molar-premolar index is 0.83. 



Discussion: As this is an exceedingly large form, next to the longest skull known, and with 

 the largest brain case of any of the species, I believe that, while its closest affinities are with 

 P. macrostegus, yet it is a distinct variety. 



Promerycochcerus marshi Thorpe 1921 

 Figs. 92-93 



Original Reference: John Day Promerycochaeri. Amer. Jour. Sci. (5), I, pp. 236-238, figs. 4 A, B. 



Type Locality: Haystack Valley, John Day Basin, Oregon. 



Geologic Horizon: Lower Miocene (upper John Day). 



Type: Holotype, Cat. No. 10999 Y.P.M., skull and jaws, still united by matrix, seven cervicals, two 

 dorsals, and proximal parts of three anterior ribs. Collected in 1876 by L. S. Davis and named in honor of 

 Professor Othniel Charles Marsh. 



Specific Characters: This skull has about the length and breadth of P. macrostegus but is 

 much more robust. The maximum zygomatic expansion is opposite the posterior part of the zygo- 

 matic foramen. The malar below the orbit is very deep and heavy, but the anterior convex prolonga- 

 tion is very feeble and does not divide the face so clearly as in P. macrostegus. The heavy 

 squamous portion of the arch rises posteriorly to the apex, which is on a line about through the 

 middle of the orbit. Its outer border is rounded and rugose. The large lacrimal fossa is deep. 

 The wide nasals are not reduced but project to a plane through the anterior portion of the canines. 

 Superiorly they were nearly straight in an anteroposterior direction and convex transversely. They 

 have been somewhat crushed downward from above but are posteriorly truncated. The wide frontals 

 are flat and unreduced and have the usual decurved supraorbital form. The orbits are small, and 

 the postorbital bar is unusually thick and massive. The temporal ridges unite above a plane through 

 the postglenoid processes, which is a point more posterior than in any other species of the genus. As 

 a consequence of this the sagittal crest is very short. The supraoccipital crest is broken away. The 

 brain case is medium-sized, low, and narrow, and lacks the prominent lateral ridges. The external 

 auditory meatus is large and directed upward as well as backward. The basicranial axis is steep 

 and the palate wide. The postglenoid process is massive, while the paroccipital process is long and 

 robust. Index: 0.63. 



Mandible: This is massive and robust. The chin profile is straight and has a symphysiodental 

 angle of 50°. The mental tubercle is large and the angle prominent. The masseteric fossa is very 

 deep, although not extensive. The condyle is very slightly inset, the coronoid process short, and the 

 sigmoid notch shallow. 



Foramina: The infraorbital foramina lie above P 4 , and the supraorbitals are 23 mm. apart. 

 The incisive foramina are large and separated by a triangular wedge of the palate, the apex of which 



