70 THE MERYCOIDODONTID/E 



versely convex. The lacrimal bone is very large, and the antorbital pits are nearly circular and very 

 deep. The frontals are very wide, medially concave, and transversely convex above the orbits, and 

 they extend well in advance of the lacrimal bones. The orbits are medium in size and circular in 

 shape. The temporal ridges unite just back of the postorbital constriction to form a low, long 

 sagittal crest whose length is about a third of that of the entire skull or slightly less. The supra- 

 occipital crest is entirely missing. The brain case is wide and well rounded, without marked ridges 

 on the parietosquamosal suture. The external auditory meatus is normal in size and position for 

 Eporeodon. The palate is wide and gently vaulted, and the U-shaped palatonarial border is oppo- 

 site the posterior lobe of M 3 . The basicranial axis is shallowly inclined. The postglenoid process is 

 of moderate size and has a nearly vertical external face. The bullx, while large, are smaller than 

 those of E. major. They are evenly rounded, except for a transverse compression, and abut against 

 the paroccipital processes. These processes are convex posterointernally and deeply concave antero- 

 externally and extend backward and outward. Index: 0.60a. 



Mandible: The symphysis is unusually wide, a character which may be due to adolescence. The 

 symphysiodental angle is apparently about 50°, and the mental tubercle is moderately large, as is 

 the angle. The coronoid process is narrow and low, and the sigmoid notch is small, with the condyle 

 not far behind the coronoid process. 



Foramina: The infraorbital foramina cannot be clearly defined, but I believe that they lie 

 above P 3 . The supraorbitals are 1 7 mm. apart. 



Dentition: P 3 and P 1 are typically deciduous. P 2 has the crown structure normal for 

 Eporeodon. The superior molars are of approximately the same diameter in both directions and 

 increase very gradually in length. The superior molar-premolar series index is approximately 

 0.76a and that of the lower series, 0.74a. I believe that these indices would be higher in the adult 

 form. 



Discussion: In the Marsh Collection there is a skull, Cat. No. 12447 Y.P.M., from Crow 

 Buttes, South Dakota, which I have provisionally referred to this species but which may be a geo- 

 graphic variant. It is fully adult but not old. Some of the differences are markedly divergent, such 

 as the obtuseness of the nasal bones which end posteriorly about 13 mm. anterior to the antorbital 

 margin. The bulla; are much larger than in the type, the palatonarial border is 5 mm. behind the 

 posterior of M 3 , the palate is much narrower, and both P 4 are somewhat oblique, with the internal 

 part forward, and the skull is considerably longer. 



Eporeodon leptacanthus (Cope) 1884 

 PI. Ill, figs. 6-8 



Original Reference: Synopsis of the species of OreodonticL-e. Proc. Amer. Philos. Soc., XXI, pp. 518- 

 519 (Eucrotaphus jacksonl leptacanthus). 



Synonym: Eporeodon occidentalis leptacanthus Merriam and Sinclair 1907. 



Type Locality: Camp Creek, John Day Valley, Oregon. Referred specimens collected at Turtle Cove, 

 Bridge Creek, Haystack Valley, and at the fossil horse beds on Cottonwood Creek, all in the John Day Valley, 

 Oregon. 



Geologic Horizon: Upper Oligocene (middle John Day — matrix green). 



Types: Holotype, Cat. No. 7695 A.M.N.H., an excellent skull, collected by the late T. L. Wortman. 

 Plesiotype, Cat. No. 11007 Y.P.M., an excellent skull and jaws. 



Specific Characters: The skull is large and dolichocephalic. The zygomata reach their 

 maximum expansion at the front of the glenoid surfaces. The malar portion is medium, but the 

 squamosal process is much lighter, with almost no posterior rise. The nasal bones are long and 

 posteriorly pointed and extend aft as far as the antorbital margin. They are ellipsoid in outline. 

 The pars facialis of the lacrimal bone is large and quadrilateral in outline and has a large, deep 

 fossa. The frontals are medially depressed and strongly convex above the orbits. They extend 



