550 



0 R E 0 D 0 N OF NEBRASKA. 



the deciduous molars, and the succeeding two permanent true molars, fully protruded, and the last yet 

 concealed within the jaw; in the latter, the deciduous and permanent true molars, except the last, which 

 had not yet protruded, form the series. 



9. An inferior canine tooth with the anterior half of its crown worn down. 



10. Nine fragments of upper and lower jaws of eight different individuals, containing true molars. 



ADMEASUREMENTS OF THE HEAD OF OREODON CULBERTSONII. 



Estimated length of the male head, from the occipital condyles to the incisive 



alveoli, ........ 93 



Estimated length of female head, ...... 88 



Greatest breadth of head at the zygoma;, . . . . .50 



Breadth at infra-orbitar foramina, ...... 19 



Estimated length of sagittal crest, ...... 34 



Length of upper molar series, ...... 40 



" lower " " ...... 39 



OREODON GRACILIS. Lekhj. 



(Tab. xi., figs. 2, 3; Tab. xiii., figs. 5, 6.) 

 Oreodon gracilis, Proc. Acad. Nat. Sci. of Philad., vol. v., p. 239. Merycoidodon gracilis, 



This species was characterized first in a verbal communication to the Academy 

 of Natural Sciences, in 1851. 



It is relatively small, the head being about the size of that of the Red Fox. 

 In Dr. Owen's collection are contained the following specimens of 0. gracilis. 



1. A cranium and face, with the base of the former and the nasal extremity of the latter broken away. 

 The specimen contains the true molars and the last premolar entire upon the right side, and fragments of 

 all the others. (Tab. xi., 2, 3.) 



2. A fragment of a face, containing on the left side the posterior two true molars. It agrees with the 

 corresponding portion of Number 1. 



3. The head of a young individual, with the posterior and upper portions of the cranium, nose, and 

 left side of the lower jaw broken away. The deciduous molars had not been shed, and the last true 

 molar remains entirely concealed within the jaw. 



Comparison of Oreodon OuTbertsonii and 0. gracilis. — Besides the great dispro- 

 portion in size of the two species, there are a few other differences to be indicated. 



In 0. Culbertsonii the sagittal crest rises in a pyramidal manner gradually from 

 the sides of the temporal fossse, but in 0. gracilis, appears only as an abruptly ele- 

 vated roughened line at the conjunction of the parietal bones. The posterior extre- 

 mities of the nasal bones are angular in the former, but convex in the latter. The 

 lachrymal depression is not quite so deep relatively in 0. gracilis as in 0. Culbert- 

 sonii, and the orbital entrance is more nearly circular in that than in this. 



The ossa tympanica are also more inflated in 0. gracilis. 



