264 DOUG LASS FOSSIL M A M M A LI A 



M. 



Lengl li of I" 006 



VV tdth of I'J 008 



Length of IP 008 



Width of M- 1 - 10 



Length of Mf ; 10 



Width of M-> 012 



Length of Mi 0093 



Width of M-i 125 



Width of nasals, greatest 0112 



Width of skull between anterior of orbits o:>0 



Diameter of lachrymal depressions, antero posterior 018 



Oreodon robustum, sp. nov. 

 Type No. 56. 



The greater part of a skull found in bed of soft sandy clay, northeast of Toston, 

 near the Missouri river, southeast of Helena. 



It is readily distinguished from other species by several characters. 



Distinguishing characters: Size large ; face and anterior nares deep vertically; nasals 

 broad; zygomatic arch broad below orbits; palate broad; foramen ovale extremely large ; 

 tympanic bulla very small and separated from basioccipital by a wide space; incisive fora- 

 mina broad oval. 



The canines agree with the general robustness of the skull in being large. The 

 crowns tire not preserved. P 1 -is narrow. V* is a little different from that of O. culbert- 

 soni. It is narrower. The anterior festoons tire smaller, there being two little pits, but 

 the ridge or partition that divides them does not continue downward on the tooth. On 

 account of the thinness of the principal cusp the posterior internal festoon encloses a 

 larger area. 



On the premaxillaries, beside the narial openings, air quite large depressions, which 

 in their centres expose a small surface of the anterior roots of the canines. It looks as 

 though the premaxillaries bad begun to coossify. The height of the anterior mires and 

 of the face are very marked. The nasals are broadest above the anterior parts of the 

 lachrymal depressions. From here they are narrowed backward very regularly, ending 

 in points. Their posterior portions form a convexity. The supraorbital foramina are 

 farther apart than in O. culbertsoni. 



The roof of the brain-case is broken away, showing part of the cast of the cerebrum 

 and cerebellum. 



The tympanic bullee are similar to those of 0. culbertsoni in form. The posterior 

 portion, which abuts against tin; paroccipital, forms a process which extends downward a 

 short distance in close contact with this larger process. Another process extends down- 



