44 



Annals of the Carnegie Museum. 



genus T. validum. Thus the fore arm of the new genus is actually a 

 little longer than in Diplacodon and is very nearly as long as that of T. 



validum, notwithstanding the much 

 smaller size of the Uinta form of 

 which we are speaking. Another 

 striking difference between the forms 

 here compared is the lateral expan- 

 sion of the proximal and distal ends 

 of the radius. In the Oligocene 

 form the shaft of the radius is more 

 rounded in the middle region, while 

 more proximally and distally a sud- 

 den expansion takes place, which is 

 also well displayed in the Uinta 

 specimen described and illustrated 

 by Scott and Osborn. In Diploceras 

 oshorni the shaft is flatter, more uni- 

 form throughout, and the proximal 

 and distal ends comparatively little 

 expanded. 



The proportions of the ulna con- 

 form to the radius and it is conse- 

 quently slenderer and proportionally 

 longer than in Diplacodon and Titan- 

 otherium. I n detail the bone is other- 

 wise quite similar to that in the two 

 latter genera, including the well defined tendinal groove on the ante- 

 rior superior angle of the olecranon process so characteristic of the 

 ulna of Titanotherium validum, but apparently less developed in the 

 Princeton specimen, judging from the illustration PI. IX, Figs. lo-ioc, 



a c). 



Measurements. 



Radius. 



No. 2862, 

 Mm. 



Greatest length 380 



Transverse diameter at middle of shaft 40 



Transverse diameter of head 78 



Transverse diameter of distal end 77 



1 2 



Fig. 9. Diploceras osborni Peter- 

 son. (Paratype. No. 2860. X g.) 

 I, lateral; 2, anterior views of radius 

 and ulna. 



Ulna. 

 Length of olecranon process 100 



