84 THE MERYCOIDODONTimE 



Discussion: Cat. No. 10143 Y.P.M. is provisionally referred to E. facificus. This skull, col- 

 lected at Turtle Cove in 1875 by L. S. Davis, is that of an old individual, probably a male. It 

 differs from the type of E. facificus mainly in that the pterygoid process of the maxilla is strongly 

 developed and posteriorly produced and ends in a blunt point; the glenoid articular surfaces are 

 wide and heavy; the bulls are smaller; the mastoid is heavy and rugose, and the paramastoid is 

 thickened, with its greater diameter oblique to the sagittal plane instead of transverse; and the 

 length of the molar series is 44 mm. and of the premolar 49 mm., but the total length of the dental 

 series, including the canine, is the same as that of the type. 



It is probable that both old age and sex together have produced these variations. Just what 

 proportion of influence each has had it is impossible to say, but the differences in the bone, i.e., 

 maxilla, glenoid, mastoid, and paramastoid, are probably due to sex; the others, such as length of 

 molar and premolar series, may well occur in old age. Another skull, Cat. No. 10147 Y.P.M. , is 

 that of an extremely old individual and exhibits some of the characters noted above. 



Three skulls, Cat. Nos. 12402-12404 Y.P.M., collected by Davis in 1875 on the North Fork of 

 the John Day River, 15 miles from its junction with the main stream, are apparently a localized 

 variety of E. facificus. Their horizon is, however, both middle and upper John Day. The 

 distinguishing characters are, very briefly, as follows: length approximately the same as that of 

 E. facificus; face broader and bizygomatic diameter greater; nasals slenderer and more elongate; 

 anterior prolongation of zygoma much more prominent, dividing the face more sharply; origin of 

 zygoma heavier and more offset from the alveolar parapet; skull generally more robust; orbits 

 more nearly round, with vertical diameter much less; brain case with about the same diameter but 

 diameter of postorbital constriction smaller; postglenoid tubercles less robust; paroccipital processes 

 extending strongly outward and downward to contact the bulls only at their base; palate much 

 wider and less vaulted and less posteriorly produced; molar series shorter, equal to or slightly less 

 than the premolar series in length, with total length of dental series less by 5 mm.; and supra- 

 orbital foramina closer together. 



Cat. No. 12401 Y.P.M. is a skull, collected by Davis in the North Fork area, but with matrix 

 of a light-chocolate color. This color of matrix is not seen in any of the specimens in the Marsh 

 Collection which were collected outside of the North Fork region, and its horizon is most probably 

 upper John Day. The distinguishing characters are, briefly: skull with marked dolichocephalism 

 and length somewhat less than that of E. occidentalis, or 1 82 mm. from the occipital condyles to the 

 prosthion inclusive; lacrimal fossa; small and very shallow; nasals extending to a point approxi- 

 mately above the incisive border; bulls small; length of molar series 48 mm. and of premolar 

 44 mm., total length of dentition 100.5 mm.; and infraorbital foramen is above anterior part of P 3 . 

 The right P 4 shows an abnormality in that it has two accessory pillars on the external face of the 

 cone, while the left P 4 is normal. 



When further material has been collected from the North Fork area it may show that this skull 

 represents a new subspecies. There is a certain lack of conformity between the North Fork speci- 

 mens and those from the Basin proper, as Cope pointed out years ago. 



The specimens of this species in the Marsh Collection indicate that 1 8 per cent attained a very 

 old age before death. 



Eporeodon parvus Thorpe 1921 

 Figs. 44-45 



Original Reference: John Day eporeodons, with descriptions of new genera and species. Amer. Jour. 

 Sci. (5), II, pp. 101-103, figs. 4-5 (Eporeodon trigonocephalm parvus). 



Type Localities: Haystack Valley (HT) and Turtle Cove (PT), John Day Valley, Oregon. 



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



Types: Holotype, Cat. No. 12425 Y.P.M., skull and jaws, collected by L. S. Davis, 1875. Paratype, 

 Cat. No. 12426 Y.P.M., muzzle and part of lower jaws, collected by William Day. 



Specific Characters: The skull is the smallest in the genus so far described. The muzzle 

 is somewhat depressed and narrow, and the highest point of the skull is above the postorbital con- 



