EPOREODON 75 



Dentition: The superior molar-premolar index is 0.87. The parastyles and mesostyles of the 

 molars are more rotated than in most of the species of this genus, and the metastyle of M 3 is very 

 poorly developed. The molars and P 3 " 4 are wider than long. 



Discussion: The basicranial area of this species shows several distinct advances over E. bul- 

 latus y such as the much larger bulls, the great increase in size of the foramen lacerum fosterius and 

 of the foramen lacerum medium, as well as the more anterior position of the latter with respect to 

 the bulla and the absence of the foramen rotundum. 



A skull and jaws, Cat. No. 12273 Y.P.M., from the upper Oligocene of South Dakota, is 

 tentatively referred to this species. It is fully as large as E. major, but it varies from that form 

 in having the posterior part of the nasal bones obtuse, the bullse less inflated, and the diameter of 

 the postorbital constriction about 5 mm. greater. 



A single specimen, Cat. No. 12400 Y.P.M., in the Marsh Collection, from Turtle Cove, John 

 Day Valley, Oregon, is referred to E. major. It is middle John Day in age and in general coin- 

 cides fairly closely, though not exactly, with this Great Plains form. 



Eporeodon major cedrensis Matthew 1901 

 PI. V, figs. 4-6 



Original Reference: Fossil mammals of the Tertiary of northeastern Colorado. Mem. Amer. Mus. 

 Nat. Hist., I, pt. 7, pp. 396-397. 



Type Locality: Castle Rock, Logan County, northeastern Colorado. 



Geologic Horizon: Upper Oligocene (Martin Canyon). 



Type: Holotype, Cat. No. 8949 A.M.N.H., skull and partial skeleton of a young individual. 



Specific Characters: This species is based on an immature skull, with partly deciduous den- 

 tition. The skull is smaller and shorter than that of E. major and is approximately the size of that 

 of Merycoidodon culbertsonii. The maximum expansion of the zygomata is in advance of the 

 glenoid surface, and the malar is moderately deep beneath the orbit. The nasals are posteriorly 

 acute. An unusual character is the apparent absence of the lacrimal fossa, which may be due to 

 adolescence. The frontal area is more convex than in E. major. The temporal ridges unite just 

 aft of the postorbital constriction to form a low sagittal crest, less than a fourth of the skull length. 

 The supraoccipital crest is posteriorly well produced, and the wings are moderately widespread. 

 The brain case is full and well rounded. The external auditory meatus is large and is upwardly 

 and backwardly directed. The basicranial axis is medium. The palate is medium in width and 

 slightly vaulted, with the U-shaped palatonarial border slightly back of the last molars. The 

 glenoid articular surface is large and gently convex. The postglenoid process has a marked oblique 

 slope downward and inward. The process is moderately large and in contact with the bulla, which is 

 mediumly inflated, with its long axis anteroposteriorly directed. The long diameter of the base of 

 the paroccipital process is transverse, while more distally the process is nearly round in section. 

 Index: 0.56. 



Foramina: The infraorbitals are very obscure but appear to be above the anterior part of P 3 . 

 The posterior palatines are opposite P 4 . 



Dentition: Matthew, in his description of the teeth, said that the "vertical length, proportion 

 of premolars to molars, individual form of premolars, especially of their external crescents, and the 

 presence of a small posteroexternal lobe on M 3 , differ from Oreodon and agree with Eporeodon 

 major." The teeth are, however, smaller than those of the latter. The molar-premolar index 

 is 0.78. 



Skeleton: This species has a smaller, slenderer skeleton and a much shorter neck than is the 

 case in either E. major or E. occidentalis. The neck, in fact, is shorter than that of Merycoidodon. 

 The pollex is absent. The scapula has a weaker metacromial process but otherwise is like that of 

 Mesoreodon. The ends of the cervical centra are flattened to oval, whereas in E. occidentalis of the 



