112 M..R. Thorpe — Netv Forms of Agriochoerus, 



Coloreodon and Agriomeryx were based on the presence 

 of three instead of four superior premolars, while Arti- 

 onyx was established on a pes and a portion of hind leg. 

 Artionyx was the basis for a new suborder, Artionychia. 

 Skeletal elements have been referred to no fewer than 

 three mammalian orders, and the peculiarities of struc- 

 ture exhibited by this genus have given rise to much 

 speculation in regard to its taxonomy and life habits. 



The writer's reasons for placing Eucrotaphus in the 

 genus now under consideration will be more fully set 

 forth in a subsequent paper, based chiefly upon Leidy's 

 descriptions and the work of contemporaneous and sub- 

 sequent students. 



The former method of classification of the species on a 

 basis of the possession of either three or four superior 

 premolars has proved unreliable. However, the later 

 forms usually have but three superior premolars. The 

 osteology of this genus and its affinities have been very 

 ably described and discussed in the papers cited in the list 

 of references. The illustrations for the present paper 

 were made by Mr. Rudolf AVeber. 



White River Species. 

 Agriochoerus antiquus antiquiis Leidy 1850. 



Middle Oligocene (lower Brule), bad lands, Nebraska. 



Specific characters. — Skull approximately the size of 

 Oreodon culhertsonii; orbits subrotund; infra-orbital 

 foramen above interval between P^ and P^ ; anterior part 

 of palate strongly uparched ; external buttresses of molars 

 hemispherical ; no internal cingulum on ]\P ; postero-inter- 

 nal lobe of P^ very small ; P^ right triangular ; P^ molari- 

 f orm but with anterior internal wall incomplete ; muzzle 

 long and narrow; bullag moderately large; superior pre- 

 molars always four; inferior incisors three, but very 

 small. 



Several specimens in the Marsh Collection have served 

 for amplification of this type, especially Nos. 12657 and 

 12666, Y. P. M. 



3Ieasurements. 



mm. 



Breadth of forehead at post orbital processes (holotype) . . . 59.2 

 Superior molar series, length (No. 12657, Y. P. M.) 47 



