DAKOTA AND NEBRASKA. 135 



different and larger species of A(/rioc7io?ru.s than the former, to which the above name 

 has been given. 



The cranial specimen nearly agrees in size, form and proportions with that origin- 

 ally ascribed to Eacrotap]uis aurifus, described in The Ancient Fauna of Nebraska, 

 and represented in figures 1 to 3, plate vii, of that work. Both specimens possess 

 large inflated auditory bulla}, which differ from those in the cranium referred to E. 

 JacJcsoni, and since to A[/rioc7iwrus antiquus, in their larger size and oval form, but 

 they also differ in some measure from each other, both in exact form and size. In 

 the specimen originally referred to E. aurifus they are the larger, and their base pos- 

 teriorly is prolonged to articulate with the base of the paramastoid process. In the 

 other specimen they are without the prolongation, and rest directly against the latter 

 process. In both specimens the basi-occipital is deeplj' carinated. 



The inferior second true molar above mentioned is like the corresponding tooth of 

 A. antiquus, but measures 8 J lines fore and aft and G lines transversely, while that of 

 the latter measures 7 lines by Sg lines. 



Agriochcerus latifrons. 



The last collection of Dr. Hayden from the Mauvaises Terres contains a specimen, 

 consisting of a nearly complete skull, including the lower jaw and teeth, which I at 

 first viewed as pertaining to Agriocliverus antiquus. It sufficiently approximates the 

 corresponding portions of the latter, both in size and constitution, to belong to it, but 

 yet in some points presents such wide differences that I shall describe it as of a dis- 

 tinct species, under the above name, though I think it may only prove to be a sexual 

 variety of the former, and perhaps belongs to the male. 



The skull oi^ Ar/riochcerus latifrons, represented in figure 1, plate XIII, has lost the 

 anterior extremity and upper part of the face, including a portion of the forehead, 

 both zygomata, and the summit of the inion. It is much fissured and is otherwise 

 somewhat mutilated, and is yet partially imbedded in its rocky matrix. It contains 

 most of the molar teeth, part of one canine, and traces of the lower incisors. 



The skull is almost the size of those of the larger, more robust, apparently male 

 skulls of Oreodon Gulhertsoni, nearly agreeing with them in size, proportions and 

 constitution. 



The cranium might readily be mistaken for that of the latter animal were it not for 

 the large auditory bulla?, of which one is exposed through an accidental fracture of 

 the specimen. The bullfe are nearly of the form and size of those of the cranial 

 specimen formerly attributed to Eucrotaplms anritus, as represented in figure 3, plate 

 vii, of The Ancient Fauna of Nebraska. 



The cranium of A. latifrons is proportionately longer than in Oreodon Gulhertsoni. 

 The sagittal crest is long, high and strong, and extends from the broad summit of the 



