100 M. R. Thorpe — John Day Eporeodons 



influence each has had it is impossible to say, but the 

 differences in the bone, i. e., maxilla, palate, glenoid, 

 mastoid, and paramastoid, as well as zygoma, are prob- 

 ably due to sex; the others, such as length of molar 

 and premolar series and mesocephaly, may well occur in 

 old age. Skull No. 10147, Y. P. M., is that of an extremely 

 old individual and exhibits some of the characters noted 

 above. 



Three specimens, Nos. 12402, 12403, and 12404, Y. P. M., 

 collected by L. S. Davis in 1875 on the North Fork of the 

 John Day River, 15 miles from its junction with the 

 main stream, are apparently the forms of E. pacificus in 

 that locality. Their horizon is, however, both middle 

 and upper John Day. Specific characters are as follows : 

 approximately same length as E. pacificus; total 

 length of tooth row less by 5 mm. ; molar series shorter, 

 equalling or slightly less than length of premolar series ; 

 postglenoid tubercles less* robust; paroccipital processes 

 extending strongly outward and downward, and in contact 

 with the bullae only at base; palate much wider and 

 less uparched; palate less produced posteriorly; incisive 

 foramina wider and less ovate ; face broader and width 

 at zygoma greater; supra-orbital foramina closer 

 together ; nasals more slender and elongate ; cranium 

 about the same width but postorbital constriction less ; 

 orbits more nearly round, with much less vertical diam- 

 eter ; anterior prolongation of zygoma much more promi- 

 nent, dividing the face more sharply ; skull more robust ; 

 origin of zygoma heavier and more offset from alveolar 

 parapet; basicranial axis less steep. 



Still another specimen. No. 12401, Y. P. M., consists of 

 a skull only, certain characters of which refer it to E. paci- 

 ficus. It was found by Davis in the North Fork area, but 

 its matrix is light chocolate in color and the horizon prob- 

 ably upper John Day. This color is not shown in the 

 matrix of any specimens in the collection outside of the 

 North Fork area. The specific characters are: skull 

 length a little less than that of E. Occident alls, or 182 mm. 

 from occipital condyles to prosthion inclusive ; markedly 

 dolichocephalic; total length of dentition, 100.5 mm., 

 length of molar series, 48 mm., and of premolars, 44 mm. ; 

 bullae small; short sagittal crest; lacrymal fossae small 

 and very shallow; infra-orbital foramen above anterior 

 portion of P^ ; nasals extending approximately to a point 



