86 



THE MERYCOIDODONTID/E 



Discussion: I originally placed this species with E. trigonocephalus, but later evidence has con- 

 vinced me that this was an unnatural relationship. This skull is almost dolichocephalic, and the pre- 

 molar series is shorter than the molar, whereas in Cope's species the skull is decidedly brachycephalic 

 and the premolar series is considerably longer than the molar. There are other important differ- 

 ences which clearly separate the two forms. 



Eporeodon socialis Marsh 1884 

 Figs. 46-64, 186} PI. XLII; PI. L, figs. 1-2 



Original Reference: Dinocerata. Mon. X, U. S. Geol. Surv., pp. 64, 187, figs. 73, 162-163. 

 (Figures of type skull and left feet, but no text descriptions.) 



Type Locality: Scotts Bluff, Nebraska. 



Geologic Horizon: Upper Oligocene (upper Brule). 



Types: Cotypes, Cat. Nos. 13118 and 13119 Y.P.M., two nearly complete skeletons. Collected by 

 M. H. Clifford and A. S. Shelley, August 17, 1874. 



Specific Characters: The skull (Fig. 46) is larger than that of Merycoidodon, is dolicho- 

 cephalic, and has a nearly straight superior contour, except for a slight convexity just back of the 

 postorbital bars. The zygomata are moderately heavy, approximately parallel to the sagittal plane, 



r.p.M. 



mfrhn. 



Fig. 46. — Eporeodon socialis Marsh. Skull and jaw. CT. Cat. No. 13118 Y.P.M. 1/2 nat. size, am, angle of 

 mandible; cp, P-, or caniniform premolar; eatn, external auditory meatus; /, frontal; */, infraorbital foramen; //, lacrimal 

 fossa; m, malar or jugal; mj, mental foramen; mp, mental prominence or mental tubercle; mx, maxilla; n, nasal 

 o, occipital; oc, occipital condyle; p, parietal; pc, parietal or sagittal crest; pg, postglenoid process or tubercle of squamosal 

 pmx, premaxilla; pof, postorbital process of frontal; pp, paramastoid or paroccipital process; s, squamous temporal bone 

 sof, supraorbital foramen; zpt, zygomatic process of temporal bone. (After Thorpe, 1931.) 



and have a marked upward slant posteriorly from beneath the orbits. The nasal bones are unre- 

 duced, and their posterior obtusely truncated ends lie about on a line through the antorbital margins 

 (Fig. 47). These bones have a nearly uniform width which decreases very slightly as they extend 

 backward. The -pars facialis of the lacrimal is large and quadrilateral in outline. The lacrimal 

 fossa is large and deep. The frontals are wide and long and have a medial concavity and a marginal 

 transverse convexity. They extend well in advance of the lacrimal bones. The orbits are medium 

 in size and look mainly outward. The temporal ridges are not prominent and unite above the 



