EPOREODON 8 1 



paroccipital processes are transversely wide and pressed against the posteroexternal side of the bulla:, 

 and they become slenderer medially and twisted on themselves distally. Index: 0.50. 



Mandible: The symphysiodental angle is 52°, and the chin profile is markedly concave. The 

 mental tubercle is prominent, as is the angle. The horizontal ramus is moderately slender, although 

 it increases gradually in depth aft. The coronoid process is low, and the condyle is inset and well 

 marked, while the sigmoid notch is moderately deep. 



Foramina: The infraorbitals lie above the anterior part of P 4 . The supraorbitals are approxi- 

 mately 18 to 20 mm. apart. The posterior palatine foramina are opposite P 4 . 



Dentition: Douglass stated that "all the upper premolar and molar teeth are longer than 

 wide," which I believe to be an error. The statement is true for P 1 , P 2 , P 3 , M 2 , and M 3 , but P 4 

 and M 1 are wider than long. All of the superior teeth of E. major, with which Douglass compares 

 his specimen, are wider than long, except P 2 , both of whose diameters are equal, and P 1 , which is 

 longer than wide. In the genotype, E. occidentalis, P 4 and the molars are of about equal diameters. 

 The superior molar-premolar series of E. m. relictus have the same proportions of length to width 

 as in E. montanus. The anterior premolars are crowded in both upper and lower dentitions. P 1 

 overlaps P 2 externally, while the inferior three anterior premolars overlap. P 4 has a nearly uniform 

 width, although in some species, E. socialis for example, the posterior part of P 4 is considerably 

 wider. The superior molar-premolar index is 0.87, and the lower, 0.78. 



Discussion: The skull of this species is midway between the dolichocephalic form of E. socialis 

 and the mesocephalic of E. major, while E. bullatus has a much more mesocephalic, almost brachy- 

 cephalic, skull. The dental indices of all of these are nearly alike. In some ways this is closest to 

 the E. major group, and particularly to E. m. relictus, but the bulla: are approximately half as large, 

 the basicranial axis is steeper, the sagittal crest is much higher and thinner, and the supraoccipital 

 crest is much more produced than in E. major itself. 



There is but one skull in the Marsh Collection referable to this species, and it is Cat. No. 

 12446 Y.P.M. It was collected at Scotts Bluff, Nebraska, on the north side of the Platte River, in 

 the same geologic horizon as the type, and shows no important variations. 



Eporeodon occidentalis (Marsh) 1873 



Figs. 41-43 



Original Reference: Notice of new Tertiary mammals. Amer. Jour. Sci. (3), V, pp. 409-410 

 (Orcodon occidentalis). 



Synonyms: Eucrotaphus major Lcidy, part; Eucrotaphus jacksoni Leidy, part; Merriam and Sinclair 



1907. 



Type Locality: Bridge Creek ?, John Day Valley, Oregon. Referred material from Turtle Cove, 

 Haystack Valley, and Bridge Creek, John Day Valley. 



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



Types: Genoholotype, Cat. No. 10142 Y.P.M., skull, collected by Rev. Thomas Condon. Plesiotype, 

 Cat. No. 12345 Y.P.M., skull and lower jaws. 



Specific Characters: The skull is smaller than that of E. major and somewhat larger than 

 that of Merycoidodon culbertsonii. It is mesocephalic but almost in the lower brachycephalic range. 

 The zygomata are moderately heavy beneath the orbits and lighter in the squamosal part, with an 

 abrupt rise beginning near the middle of the zygomatic foramen. The maximum expansion is 

 approximately at the postorbital constriction. The nasal bones are posteriorly acute to acutely trun- 

 cated, extending posterior to the antorbital margin. They are somewhat ellipsoidal in shape. The 

 lacrimal bone has a large pars facialis, roughly quadrilateral in outline, and bears a large, deep fossa, 

 confined wholly to the lacrimal. The frontals are wide and flat, with a slight median concavity and 



