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 bulle to the genus Hucrotaphus, there remain the two species origi- 
nally referred to Oreodon by Leidy, the O. culbertsoni and the O. gracilis. 
To these Leidy subsequently added two others, the O. affinis, which is in- 
termediate in size between the two named, and the O. Aybridus, of larger 
size than either. As the condition of the otic bull in the last is unknown, 
its generic reference is not certain. AJ] 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 O. culbertsond, abundantly 
represented. Besides these there is a form intermediate between the 0. 
gracilis and the O. affinis, which is nearer the former than the latter. Of 
O. gracilis there are two skulls complete; of the form next larger, which 
Teall 0. gracilis coloradoénsis, two complete crania (one with skeleton), 
and a face with teeth. Of a form between the 0. afinis and the 0. 
culbertsoni, there are four skulls complete (two with skeletons) ; and of 
O. culbertsoné 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. .085 
in length; canine and premolars .080; 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 
OL OTDIGS LOMB ei v's ic SO Gaia Due ee aie a Weare cd O. coloradoénsis, 
Nasal bones obtuse posteriorly, frontals little produced on 
either side of them; true molar teeth not exceeding .038 ; 
front at orbits .057 in width. ........ Mirch Wario sheik cs Vieay wie CN TIOIDs 
Nasal bones acute posteriorly ; frontal produced to an acute 
apex on each side of them; molar teeth .040; front, .056. 
O. periculorum. 
Nasals and frontals as last ; molar teeth .047 ; front, .0504-.. O. culbertsoni. 
PROC. AMER. PHILOS. soc. xxt. 116. 3M, PRINTED JUNE 6, 1884. 
