Cope. | 518 (Jan, 18, 
formations fails to reveal any characters distinguishing them as more than 
one species, In fact the variation in various respects is greater among the 
individuals of the John Day epoch, than between those of the two epochs. 
This was by far the most abundant mammal of the John Day epoch 
while it appears to have been rare during that of the White River. 
Specimens differ in the size of the preorbital fossa irrespective of other 
differences. ‘In some specimens it is wide and profound, including the 
lachrymal bone; in others it is less extensive and is shallow, involving but 
part of the lachrymal. It is never wanting or obscure. For estimation of 
other characters, I select ten crania, nine from Oregon and one from 
Dakota, as expressing the greatest range of variation. Of these, three 
display a peculiarity in the form of the otic bulla, Instead of being con- 
tracted backwards in front, it is protuberant and full at its inferior anterior 
part. Five other crania, agreeing with:these three in other respects, 
possess the normal form of bulla. In one cranium, which is rather more 
robust than the others, the infraorbital foramen is a little posterior to its 
usual position, being above the anterior part of the fourth premolar. 
This tooth is also distinctly smaller than in other specimens of otherwise 
similar dimensions. The majority of specimens range nearly alike in 
dimensions, but there are forms distinctly larger and smaller, which may 
represent distinct species. This question can be better decided when the 
skeletons are known. I give three sub-species which are defined as fol- 
lows: 
Length of cranium M. .197; of molar series M. .086; long 
diameter of base of paroccipital process transverse ; its pos- 
MOTTON OABE: MAU ies valve as ole stb areca uy Mua Pele vivevus din gugOnBOovits 
Length of cranium M. .219; of molar series M. .091 ; paroccipi- 
TAY PLOCEBB AG ADOVE. oc, eseee eves due Daub e aoe debi ree ciodin Jy DUCUICUs. 
Length of cranium, M. .235; of molar series, M. .099; paroc- 
cipital process strongly compressed, its posterior base an. 
Pulate Omthe middlegiMeyti sic iis i « cour ee Lj. leptacanthus. 
The above measurements of length are made from the occipital condyles 
to the premaxillary border inclusive. . 
The three forms may represent good species. The Z. j. jacksoni is of the 
size of the Oreodon culbertsoni ; the H. j. leptacanthus is larger than the #. 
major, While the H. j. pacificus is intermediate between the two. 
Eucrotaphus jacksoni jacksoni Leidy. 
The typical specimen of the Oreodon bullatus Leidy agrees so nearly with 
the original type of Hucrotaphus jacksoni, that I cannot doubt their pert- 
inence to the same species. There are two specimens in the collection of 
the Philadelphia Academy, besides the last named, and at least one in the 
museum at Princeton, A specimen from the John Day, Oregon, cannot 
be distinguished from these. It agrees with Marsh’s measurements and 
description of his Oreodon occidentalis, and no doubt represents it. Its 
