134 ON THE EXTINCT MAxMMALlA OF 



The descending crescentoid summits of the outer lobes terminate differently from 

 those of Oreodoa. The anterior horn of the outer front lobe ends at the base of the 

 corresponding inner lobe. The posterior horn turns up to the posterior side of the 

 latter. The anterior horn of the outer back lobe joins the contiguous horn of the 

 lobe in advance below and before its termination The posterior horn ends in two 

 branches, one joining the posterior face of the inner back lobe, the other joining its 

 base posteriorly. In the last molar the latter branch does not exist, and the former 

 is joined by the contiguous horn of the horse-shoe-like summit of the fifth lobe. 



The lower last premolar is like the true molars, except that the IVont outer lobe is 

 relatively better developed than in the succeeding tooth, and is continued by a strong 

 process inward at the fore part of the crown. The inner lobes also, in comparison 

 with those of the true molars, are much reduced in size, and occupy the hinder two- 

 thirds of the inner side of the crown. See fig. 4, pi. XIII. 



The lower penultimate premolar has a single lobed crown larger than those of the 

 tooth behind. It is pointed, convex externally, sloping antero-internally, and pro- 

 vided with an ovoidal cul-de-sac postero-internally. See fig. 4, 



Several mutilated cranial portions of skulls, originally referred to a genus under 

 the name oi Eucwtaphus, of which two species were distinguished, from a difference 

 in size of the specimens and a variation in size and form of the auditory bullae, 

 under the names of E. JacJisoni and E. auritus, I supposed to belong to Agriochcerus. 



The specimens are described on page 50 of The Ancient Fauna of Nebraska, and 

 represented in plate vii of that work. They have nearly the size, proportions, form 

 and constitution of the cranium of Oreodun Cidbertsoni, but are more abruptly 

 narrowed in advance of the squamosals than is usual in the latter, and the auditory 

 bulla3 are proportionately as large as in Oreodon major. 



In the smaller of the two specimens, supposed to belong to Agriochcerus antlquus, 

 the auditory bulla3 are mammillaform, with little difference in the diameters. In a 

 better preserved cranial specimen, brought from the Mauvaises Terres by Dr. Hayden, 

 but with the auditory bullaa broken away, the cranium is somewhat narrow at its 

 fore part. In most of its details it agrees with the cranium of Oreodon Culhertsoni. 

 The sagittal crest is thirty-four lines in length from the inion, and at its bifurcation 

 receives the angular summit of the frontalis. 



For the comparative measurements of the facial specimen of Agriochoer-iis antiquus, 

 see the table following the account of A. latifrons. 



Agriochcerus major. 



A small fragment of a lower jaw containing a second true molar tooth, and a speci- 

 men consisting of the greater part of a mutilated cranium, brought from the 

 Mauvaises Terres of White River by Dr. Hayden in 1855, were supposed to indicate a 



