M. R. Thorpe — New Forms of Agriochcerus. 113 



Inferior dental series with P^, length (No. 12666, Y. P. M.) 104 



Inferior molar series, length (No. 12666, Y. P. M.) 53 



Inferior premolar series, length (No. 12666, Y. P. M.) 27 



Depth of ramus below middle of M3 (No. 12666, Y. P. M.) . . 44.5 

 Depth of ramus below middle of P3 (No. 12666, Y. P. M.) . . 32 



Agriochcerus antiquus dakotensis, subsp. nov. 



(Fig. 1.) 



Holotype (skull). Cat. No. 10106, Y. P. M.; paratype (jaws), Cat. No. 

 12665, Y. P. M. Middle Oligoeene (lower Brule), South Dakota. 



Specific characters. — Skull approximately the size of 

 A. antiquus antiquus; palate more steeply uparched, espe- 

 cially between the premolars ; P^ rotated forward and set 

 obliquely in maxilla; P^ almost an equilateral triangle in 

 basal outline; infra-orbital foramen above interval 

 between P^ and P^ ; four superior premolars. The bullae 

 extend forward to the glenoid surface and but slightly 

 below it. They are in contact with the postglenoid 



fO/06 , TYPE 

 Y. P. M. 



Fig. 1. — Agrioclioerus antiquus dakotensis, subsp. nov. Holotype. Eight 

 half, palatal view. Basal outline of bulla drawn from opposite side. 



Xl/2. 



tubercle and paramastoid process as well as the glenoid 

 articular surface. Superior contour of skull nearly 

 straight, the muzzle being of the same depth as the cra- 

 nium ; orbits small and round ; an osseous ridge, depend- 

 ing from the squamosal and parietal bones, and extending 

 from the glenoid articular surfaces to the pterygoid pro- 

 cesses, encloses a basicranial depression. This peculiar- 

 ity I have not seen in any other species. The sagittal 

 crest is moderately long. 



