1884.] 511 [Cope. 



with the carpus, tarsus and feet, with the exceptions above noted, are now 

 described for the first time. 



This genus appears first in time in the known history of the family, and 

 presents us with its primitive or least specialized characters, or those 

 nearest the average condition of the ordinary primitive ungulate. 



Species. The species of this genus are difficult to discriminate from the 

 evidence of crania alone, and their true number will remain uncertain 

 until we can study entire skeletons. My material enables me to make 

 some progress in this direction. After the removal of the forms with in- 

 flated bullae to the genus Eucrotaphus, there remain the two species origi- 

 nally referred to Oreodon by Leidy, the 0. culbertsoni and the 0. gracilis. 

 To these Leidy subsequently added two others, the 0. affinis, which is in- 

 termediate in size between the two named, and the 0. hybridus, of larger 

 size than either. As the condition of the otic bullae in the last is unknown, 

 its generic reference is not certain. All these forms are from the White 

 River epoch of Dakota, Nebraska and Wyoming. 



My material is largely from the White River beds of Colorado. I find 

 from this region the true 0. gracilis and the 0. culbertsoni, abundantly 

 represented. Besides these there is a form intermediate between the 0. 

 gracilis and the 0. affinis, which is nearer the former than the latter. Of 

 0. gracilis there are two skulls complete ; of the form next larger, which 

 I call 0. gracilis coloradoensis, two complete crania (one with skeleton), 

 and a face with teeth. Of a form between the 0. affinis and the 0. 

 culbertsoni, there are four skulls complete (two with skeletons) ; and of 

 0. culbertsoni proper, numerous parts of skulls with teeth, but none com- 

 plete. No other regions which I have explored have produced these 

 species ; not even the Ticholeptus beds, where they might have been rea- 

 sonably expected to occur. 



The distinction of the previously known species will remain as Leidy 

 has left it, with certain reservations in the matter of dimensions ; while I 

 add two sub-species. 



Nasal bones obtuse posteriorly ; frontals little produced on 

 either side of them ; true molar teeth not exceeding M. .035 

 in length ; canine and premolars . 030 ; width of front .046. 0. gracilis. 



Nasal bones obtuse posteriorly, frontals little produced on 

 either side of them ; true molar teeth not exceeding .037 in 

 length ; canine and premolars .039 ; width of front at middle 

 of orbits .046 0. coloradoensis. 



Nasal bones obtuse posteriorly, frontals little produced on 

 either side of them ; true molar teeth not exceeding .038 ; 

 front at orbits .057 in width O. affinis. 



Nasal bones acute posteriorly ; frontal produced to an acute 

 apex on each side of them ; molar teeth .040 ; front, .056. 



0. periculorum. 



Nasals and frontals as last ; molar teeth .047 ; front, .050-}-. . 0. culbertsoni. 



PROC. AMER. PHILOS. SOC. XXI. 116. 3M. PRINTED JUNE 6, 1884. 



