1884.] Old [Cope. 



Academy Philada., 1853, 392 ; 1854, 35, 157 ; 1857, 89 ; Bronn Lethsea 

 Geognostica, 1856, 930. Extinct Fauna Dakota and Nebraska, 1869, p .86 ; 

 PI. VI, fig. 1 ; VII fig. 2 ; IX, figs. 1-2. Merycoidodon culbertsoni Leidy, 

 Proceeds. Acad. Phila., 1848, 47, PI. II ; 1850,121; 1851,239. Oreodon 

 priscum Leidy, Proceed. Phila., Academy 1851, 238 ; Cotylops speeiosa 

 Leidy, Ibidem 239 ; Oreodon robustum Leidy, Ibidem 276. 



The White River epoch of Dakota, Nebraska, Colorado and Wyoming. 



The two sub-species are defined as follows : 



Length of superior true molar series from M. .040 to .042 



0. c. periculorum. 

 Length of superior true molar series from .046 to .050. . . . 0. c. culbertsoni. 



Oreodon culbertsoni periculorum Cope. 



This smaller race or sub-species has as yet only been found in the 

 White River beds of Colorado and Wyoming. I do not detect any differ- 

 ences between it and the Nebraska form other than those of size. The 

 largest measurement of the 0. c. culbertsoni given in the above table is 

 derived from Leidy ; my largest specimen gives .047 as the length of the 

 true molar series. 



Oreodon culbertsoni culbertsoni Leidy. 



Very abundant in the White River formation of Dakota, Nebraska, 

 Colorado and Wyoming. 



EUCROTAPHUS Leidy. 



Proceedings Academy Philada., 1850, p. 92. Ancient Fauna of Nebraska, 

 Smithsonian Contrib. to Knowledge, 1853, p. 56. Eporeodon Marsh, Amer. 

 Journ. Sci. Arts, Vol. ix, 1875, p. 249. 



Premaxillary bones distinct from each other. Otic bulla swollen. No 

 prelachrymal or nasal vacuities. 



This genus presents us with the first step in the series of modifications 

 which the primitive form underwent with the advance of geological time. 

 It appeared contemporaneously with the earliest representatives of the 

 family, i. e., in the White River epoch, but in small numbers. In the 

 succeeding or John Day epoch the genus Oreodon had disappeared, and 

 the present form had multiplied enormously in individuals, if not in 

 species. Subsequent to that epoch it is unknown. 



The greater number of the Oreodont remains found in Oregon belong to 

 this genus. The Eucrotaphus jatksoni bore the same relation to the Oregon 

 John Day fauna, as the Oreodon culbertsoni did to that of the White River 

 epoch. 



The species of Eucrotaphus are distinguished as follows : 



I. Palatonareal border well posterior to posterior edge of maxillary 

 bones. 



