DAKOTA AND NEBRASKA. 139 



and A. major (see pages 134, 135), with that of A. latifrons, tliey are observed to 

 bear a nearer resemblance to that of Oreodon Cidhertsoni, save in the possession of 

 largely inflated tympanies. 



In one specimen, retaining part of the forehead, the fronto-parietal suture com- 

 mences within the division of the sagittal crest, as in A. latifrons, which is exception- 

 ally the case in 0. Culbertsoni. In two specimens, retaining the inion, neither 

 possess the large lateral fossse noticed as present in A . latifrons. In one of these the 

 inion is identical with the ordinary form of that of 0. Culbertsoni ; in the other the 

 sides are depressed rather peculiarly, so as to produce nearly vertical planes. In 

 none of the specimens is the interval between the post-glenoid tubercle and the 

 paramastoid so Avide as it is in A. latifrons, and in this respect they agree with 

 0. Cidhertsoni. 



There are three additional specimens of mutilated crania, with large auditory 

 bullae and otherwise resembling those above indicated, which accompanied the skull 

 of Agriochcerus latifrons in Dr. Hayden's last collection. These specimens, like the 

 former, resemble the cranium of Oreodon more than they do that pertaining to the 

 skull of A. latifrons. They difier more or less from one another in the same manner 

 as the former cranial specimens. The auditory bullae differ remarkably in size ; in 

 one being nearly double the volume they are in a second, and being intermediate in 

 size in the third. 



All the isolated cranial specimens, — resemlaling the cranium of 0. Culbertsoni in 

 its form, proportions and construction, but having the tympanies much inflated, — I 

 was led to suppose belonged to Agriochoirus, and from the difl'erence observed between 

 them and that of A. latifrons, considered them as pertaining to the other two species 

 indicated. Since the discovery of the specimen of a skull which presents all the 

 characters previously attributed to Oreodon Culbertsoni, except in the possession of 

 large auditory bullae, described under the caption of 0. bullatus, the determination 

 is rendered doubtful. As the isolated cranial specimens, independently of the 

 presence of the greatly inflated tympanies, resemble the cranium of the ordinary 

 forms of Oreodon Culbertsoni more than they do that pertaining to the skull of 

 Agrioclioerus latifrons, they may be inferred to belong to the same category as the 

 skull referred to 0. bullatus. 



Dr. Hayden's last Mauvaises Terres collection further contains fragments of the 

 jaws with teeth of several different individuals of Agriochonnis, which agree in their 

 anatomical characters with the corresponding parts of the specimens previously 

 described, except that they vary slightly in size. A fragment of the lower jaw con- 

 taining the last two molars has a greater depth, and the teeth are larger than in the 

 specimens referred to A. antiquus and A. latifrons, but the second molar tooth is 

 intermediate in size to that of these species and that referred to A. major. 



