Cope.] 506 |Jan, 18, 
resenting two crescents, of which the anterior has its posterior horn 
developed as an obliquely transverse crest directed inwards. Last true 
molar with a heel composed of two columns. 
In the superior temporary dentition the last premolar has the form of the 
first permanent true molar. The third premolar has five lobes, 7. ¢., four 
crescents and an anterior odd one. The other temporary premolar resem- 
bles that of the permanent series. The last inferior temporary premolar has 
the three pairs of lobes usual in the Artiodactyla, and the two which pre- 
cede it resemble the corresponding permanent teeth. Says Leidy :* ‘‘The 
permanent true molars successively protrude and occupy their functional 
position before any of the deciduous molars are shed. The displacement of 
the latter by their permanent successors appears to begin with the eruption 
of the last of these, which is followed by those in advance. The first 
permanent premolar of the upper jaw appears to have protruded after the 
deciduous teeth, and occupied a position with them in the functional series, 
but remains after these are shed.”’ 
The cranial characters which belong to Oreodon as a genus are the fol- 
lowing: Orbit completed behind ; temporal fosse separated by a sagittal 
crest. A lachrymal fossa, but no facial nor frontal vacuities. Premaxil- 
lary bones distinct from each other and from the maxillaries. Nasal bones 
well developed. Auditory bulle not inflated. 
The preceding dental and cranial characters have been pointed out by 
Leidy in his various paleontological works. On account of the absence 
of the necessary material he was unable to give the characters of the 
remaining parts of the skeleton. These are of course necessary to a 
correct, estimate of the affinities of the genus, and I will endeavor to add 
such information as my material will permit. This consists of numerous 
more or less complete skeletons found in connection with the skulls by 
myself in Colorado in 1878. 
Vertebre. The cervical vertebree are rather short, and the character of 
the articulation of the centra slightly opisthocoelous, and the articular 
faces are quite oblique. The axis is the longest vertebra; the three last 
centra are subequal in length. In one of my series the seven cervicals 
are preserved. In all of these, excepting the seventh, the bases of the 
diapophysis are perforated by the vertebrarterial canal. In the sixth 
vertebra, the decurved parapophyses are especially robust. The axis and 
three succeeding centra display strong hypapophyses at their posterior ex- 
tremities, which are carried forwards as strong median keels. The odon- 
toid process is depressed so as to have a lenticular section ; it is not exca- 
vated above, but in my largest specimen the internal borders of the facets 
for the atlas are continued so as to enclose a short groove on each side at 
its base. In one smaller and immature specimen this is wanting. The 
vertebrarterial canal of the axis is enclosed as in the other cervicals. The 
canal for the second spinal nerve hasa narrow roof, but there are no canals 
* Ancient Fauna of Nebraska, p, 44. 
