Cope. | 520 (Jan, 18, 
Extinct, Mammalia, Dakota and Nebraska, 1869, p. 99, Pl. VII, fig..i; 
VIII. Hporcodon major Marsh, Am. Journ. Sci. Arts, 1875, p. 250. 
I find this species to differ in the external position of the paroccipital 
process, as related to the otic bulla, from the HZ. jacksoni. I might add that 
it differs in dimensions from all excepting the 2. jacksoni pacificus. In 
the #. jacksoni the base of the paroccipital process.is in the same line as 
the interior base of the otic bulla. In the Oregon form of the . major 
the base of the paroccipital process is much flattened, so as to be trans- 
verse, and its internal border is on the external side of the extremity of the 
large swollen bulla. ‘This species differs also from the W. jacksond in the 
median vertical carina of the occipital bone above the foramen magnum, 
a region which is in the H. jachsoni broadly flattened.’ Besides these 
points I do not notice any divergence from the #. jacksoni, with which it 
agrees in the various characters in which the latter differs from the #. 
trigonocephalus. 
The Nebraska and Oregon forms do not agree in all respects. Thus, 
while the dimensions of the dental series are the same in both, the frontal 
region is more elongate in the Oregon animal, giving greater length to the 
skull. The third superior premolar has a somewhat different form in the 
two. They may then be characterized as follows : 
Dental series M. .125; skull .224 ; third superior premolar, sub- 
CEPATRULA Te aie: a \ecwy ne, 918 Pes K RRL e Sube hg Ubi Wi busiiltay oH noe MK dubce as gn Snes H. m. major. 
Dental series M. .125.; skull .240; third superior premolar sub- 
QUACTALC co osecercesecmevinenensleceavns set neg seeee elt, m. longifrons. 
Eucrotaphus major major Leidy. 
Known only as yet from the White River epoch of Nebraska and Dakota. 
Eucrotaphus major longifroms Cope. 
Known from a single skull from the North Fork of the John Day river, 
Oregon, found by Charles H. Sternberg. It may bé observed here that 
the Oreodontide of this locality are mostly distinct from the species of 
the John Day river proper. by 
MERYCOCHGRIUS Leidy. 
Report U. 8. Geol. Survey Terrs., I, 1878, p. 202. Bettany, Quart., 
Journ. Geol. Soc. London, 1876, p. 262; Cope, American Naturalist, 1884, 
p. 281. Leidy, Extinct Mammalia of Dakota and Nebraska, 1869, p. 110 
(momen nudum). Proceedings Academy Philadelphia, 1858, p. 24 
(nomen nudum). 
As indicated in the analytical table at the head of this article, I can only 
distinguish this genus from Mucrotaphus by the confluence of the pre- 
maxillary bones. The position of the external infraorbital foramen can- 
not be regarded as furnishing generic characters, especially as it displays 
considerable variation and gradation, Some,of the species are in this 
respect quite identical with species of Merychyus (1, superbus), while others 
