DAKOTA AND NEBRASKA. 129 



major, excepting that in the specimens under observation, the inner lobes of the last 

 molar are better defined from each other internally, as in the case of the true molars 

 in advance. 



Leptauchenia nitida. 



A third species o^ Leptauchenia, smaller than the others, is founded on a mutilated 

 skull, which, together with a number of bones and fragments of other parts of the 

 skeleton, is imbedded in a mass of matrix similar to that adhering to and enveloping 

 the fossils of the other species. The specimen was obtained in Dr. Hayden's expedi- 

 tion of 1866, on White Earth Creek, a tributary of White River. 



The skull, represented in figure 21, plate XII, is about the size of that of the Musk 

 Deer, and nearly resembles that of i. major in its form and proportions. 



The cranium nearly resembles that of the last-named species, but apparently is 

 proportionately less depressed. The forehead is proportionately as large, but is less 

 prominent in the middle and more elevated at the supra-orbital margins. The 

 vacuities of the face do not encroach upon it so much as in Z. major or L. decora, and 

 appear not to have extended quite so far back on a line with the ant-orbital margins. 

 Comparatively they but slightly notch the frontals, and the prolongation of these to 

 articulate with the nasals is short. As in the other species, the vacuities appear to 

 extend above and in advance of the lachrymals. 



The orbits appear to be formed as in Oreodon. Large concave fossae impress the 

 facial surface of the lachrymals. 



The supra-orbital foramina are situated back of the middle of the position of the 

 orbits, and rather nearer the supra-orbital margin than the median frontal suture. 

 The infra-orbital foramen is situated above the fourth premolar, as in Merychyus 

 elegans. 



The face in advance of the orbits appears to be proportionately much narrower 

 than in L. decora. It was quite as narrow as that of the Musk Deer, or even 

 narrower between the position of the jaw and nose. 



The auditory buUas agree in their proportions with those of the preceding species. 



The glenoid cavity resembles that of Oreodon, but the post-glenoid tubercle is pro- 

 portionately very small. In Oreodon it is a pi'ocess of the squamosal, but in Leptau- 

 chenia nitida it appears to receive a considerable contribution from the tympanic. 



The lower jaw, as may be seen by a fragment retaining the condyle and coronoid 

 process, together with an impress of the remainder of the ascending ramus on the 

 matrix, figure 21, resembles in its construction the corresponding part in Oreodon. 



The molar teeth of the upper jaw are partially retained on one side of the specimen, 

 but are too much mutilated to determine their characters. So far as can be 



17 



