Peterson : A New Titanothere from the Uinta Eocene. 43 



deltoid groove is deep and well defined, as in the Oligocene genus. 

 On the other hand the deltoid ridge, though very prominent, does not 

 terminate in the heavy recurved process as in T. validum, but descends 

 much more gently towards the 

 supratrochlear fossa. Distally 

 there is less variation between 

 the two forms here compared. 

 The anconeal fossa in the spe- 

 cies under description is rela- 

 tively broader and the supina- 

 tor ridge is less rugose. The 

 trochlea is slightly deeper, but 

 not more oblique than in T. 

 validum. 



The humerus as described 

 and figured by Osborn holds 

 an intermediate position be- 

 tween the Oligocene genus and 

 the present form. This is es- 

 pecially shown in the develop- 

 ment of the deltoid ridge, which 

 in the Princeton specimen is 

 considerably more developed 

 than in the genus under de- 

 scription. 



Measurements. 



Humerus. 



No. 2860, No. 2861, 



Mm. Mm. 



Length from head to distal end 365 3^5 



Transverse diameter of lower part of deltoid ridge loS''' no" 



Transverse diameter at broadest portion of supinator ridge, iis 113 



Transverse diameter of distal trochlea 78 



Both radii and ulnae are represented in No. 2860. A third radius 

 was also found in the same sandstone ledge in close proximity to the 

 spot where Nos. 2858 and 2859 were found. 



The radius and ulna are long and relatively slender, when compared 

 with those of the Princeton specimen of Diplacodon and the Oligocene 



" The shafts of the two bones are more or less crushed and the measurement 

 is only approximately correct. 



Fig. 8. 



2 



Diploceras osborni Peterson. 

 (Paratype. No. 2860.) X i- Humerus, i, 

 anterior view; 2, posterior view. 



