132 ON THE EXTINCT MAMMALIA OF 



AGRIOCHOERUS. 



Agrioclioerus is a remarkable genus of extinct ruminants, more aberrant from exist- 

 ing members of the order than any of those previously described. It was originally 

 characterized on fossil remains of a species from the Mauvaises Terres of Dakota, 

 presented to this Academy by Dr. Hiram A. Prout, of St. Louis. 



Agriochcerus antiquus. 



The remains on which the species was founded distinguished by the above name, 

 consist of the greater portion of the anterior part of a skull, including portions of both, 

 jaws with most of the molar teeth, and small fragments of jaws with teeth of a second 

 individual. The former specimens, much mutilated, are represented in figures 5, 6, 

 plate i, of The Ancient Fauna of Nebraska. Several of the latter, in a better state of 

 preservation, are represented in figures 9, 10, of the same plate. 



The specimens indicate an animal with the skull approximating in size that of 

 Oreodon Culhertsoni, 



The face appears to have been shorter and of less depth in relation with its breadth, 

 than in the latter. The forehead had nearly the same form but is flatter, and is 

 somewhat abruj)tly depressed on each side above the position of the post-orbital 

 processes. 



The frontals posteriorly, though broken away, are readily observed to have been 

 convergent and received into a notch of the parietal as in Oreodon. Anteriorly they 

 are too much broken to judge of their arrangement. 



The supra-orbital foramina are small, and quite near the inter-frontal suture. 



The orbits are sub-rotund, relatively about as large as in Oreodon, but with rather 

 more obliquity upward. They are open behind, as in Anoplotherium, the carnivora 

 generally, etc., and in this respect differ widely from those of ordinary ruminants. 

 The post-orbital processes of the frontal and malar bones are conoidal, of nearly equal 

 size, and are about half an inch apart at their ends. 



No lachrymal fossa exists in front of the orbit, the facial surface of the lachrymal 

 bone contributing to the general convexity of the side and upper part of the face. 



The infra-orbital arch is proportionately almost as deep as that of Oreodon, It has 

 nearly the same form, but has its external face more A'ertical. Between it and the 

 alveolar border the face is less depressed than in Oreodon. 



The infra-orbital foramen occupies a position above the interval of the posterior two 

 premolars. 



The hard palate, for the greater extent obscured in the specimen by a remaining 

 portion of matrix, at its fore part is deeply inclined at the sides. 



