138 



THE MAMMALIA OE THE DEEP KIV^ER BEDS. 



This shape is already well shown in the White River species and is marked by its 

 relatively great transverse breadth, prominent internal epicondyle, broad, rounded 

 intercondylar ridge, which is nearly median in position, and the nearly equal width 

 of the external and internal divisions of the trochlea. The anconeal fossa is relatively 

 higher and narrower than in JEporeodon. 



Some differences, which are probably of a sexual nature, are to be observed in 

 the proximal end of the humerus in different specimens. In those which are asso- 

 ciated with the skulls marked by small canines, and therefore presumably female, the 

 head is more hemispherical and markedly shorter in the antero-posterior direction ; 

 the external tuberosity extends less completely across the anterior face of the bone 

 and the bicipital groove is wider. Possibly, however, these distinctions are specific 

 rather than sexual. 



The ulna and radius (PI. V, Fig. 38) are massively constructed ; they are en- 

 tirely unreduced and show no tendency to coossify at any point. The radio-ulnar 

 arch is very long, extending from a short distance below the head to the distal ex- 

 pansion ; this is not visible in the anterior view. The radius has the form of head 

 which is characteristic of the family and therefore requires no detailed description. 

 The shaft is not so broad and antero-posteriorly compressed as in Eporeodon, but 

 more rounded and cylindrical in the middle, reverting thus in some degree to the 

 condition found in Oreodon. The distal end is more expanded transversely than in 

 JEJporeodon, though in this respect there is considerable variation. The scaphoid sur- 

 face is peculiar in the deep groove on its ulnar border. This is already indicated in 

 the Oregon genus, but to a much less conspicuous degree, especially in the breadth 

 and depth of the groove behind. A similar groove appears in Merycliyus. The lunar 

 facet is like that of JEporeodon, but is less closely connected with the scaphoid facet. 



The ulna is quite unreduced and has a very heavj* shaft, which almost equals 

 that of the radius in antero-posterior thickness and exceeds it in width. The olecra- 

 non is high and massive. The distal end is excavated to receive the expansion of 

 the radius and carries a facet for the cuneiform, which is narrow antero-posteriorly 

 but broad transversely. This ulna differs but slightly and in no important respect 

 from that of JSporeodon. 



The manus (PI. V, Figs. 39, 40) presents some features of much interest, as 

 here we find most strongly emphasized the tendency towards Merycliyus which is 

 more obscurely indicated in the structure of the skull and teeth. In the carpus the 

 scaphoid has undergone some noteworthy changes as compared with that of the more 

 ancient genera. It is increased in size, especially in breadth ; the radial surface is, 

 as usual, concave behind and convex in front, but rises more towards the ulnar bor- 



