Cope.] 520 • [Jan. 18, 



Extinct Mammalia, Dakota and Nebraska, 1869, p. 99, PI. VII, fig. i ; 

 VIII. Eporeodon 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 E. jacksoni. I might add that 

 it differs in dimensions from all excepting the E. jacksoni pacificus. In 

 the E. 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 E. 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 E. jacksoni in the 

 median vertical carina of the occipital bone above the foramen magnum, 

 a region which is in the E. jacksoni broadly flattened. Besides these 

 points I do not notice any divergence from the E. jacksoni, with which it 

 agrees in the various characters in which the latter differs from the E. 

 trigonocephalies. 



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- 

 triangular. E. m. major. 



Dental series M. .125 ; skull .240 ; third superior premolar sub- 

 quadrate E. m. longifrons. 



Encrotaphus major major Leidy. 

 Known only as yet from the White River epoch of Nebraska and Dakota. 



Eucrotaplms major longifrons Cope. 



Known from a single skull from the North Fork of the John Day river, 

 Oregon, found by Charles H. Sternberg. It may be observed here that 

 the Oreodontidse of this locality are mostly distinct from the species of 

 the John Day river proper. 



MERICOCHCEHUS Leidy. 



Report U. S. Geol. Survey Terrs., I, 1873, 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 

 (nomen 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 Eucrotaphus 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 (M. superbus), while others 



