78 



TRANSACTIONS OF WAGNER 



UINTA SELENODONTS 



course is nearly straight, except for a slight eversion of the distal end. 

 Near the distal end the shaft is slightly contracted, becoming more rounded 

 in shape, but expands again just above the trochlea. The latter is sub- 

 spheroidal in shape and has quite a prominent palmar carina ; it is demarcated 

 from the shaft by a narrow but distinct groove. 



Metacarpal iii. considerably exceeds the second both in length and thick- 

 ness, though not so much as is usual among the selenodonts, even of this early 

 period. Except for the projection which abuts against the unciform, the head 

 is not expanded and is no broader than the shaft, and even this projection, 

 though it has quite an extensive contact with the unciform, reaches but slightly 

 across the head of mc. iv. There is, of course, no articulation with the trape- 

 zoid, which is prevented by the articulation, small as that is, of mc. ii. with the 

 magnum. The facet for the magnum is almost plane transversely, as it also is 

 in Leptorcodon, while in Protylopas this surface is quite deeply concave. The 

 tubercle for the attachment of the extensor carpi radialis muscle is larger and 

 more rugose, though not more prominent than in the last-named genera. The 

 shaft is straight and of almost uniform diameter throughout, though broaden- 

 ing slightly above the distal trochlea, and for the greater part of its length the 

 dorsal surface is rounded and convex. The trochlea is low, of subcylindrical 

 form, and the carina is altogether palmar in position. 



Metacarpal iv. differs in a few details from mc. iii. It is a little shorter, 

 for the proximal end does not rise so high, owing to the downward extension 

 of the unciform ; distally also it ends at a level slightly above that of mc. iii. 

 The head, which articulates only with the unciform, is, of course, differently 

 shaped, and the dorsal surface of the shaft is plane or very faintly concave, 

 instead of convex. The distal trochlea also is rather more spheroidal than 

 that of mc. iii. 



MEASUREMENTS. 

 Carpus, breadth . 



" height in median line 

 Mc. ii., length 



" breadth, proximal end 

 " distal end . 

 Mc. iii., length 



breadth, proximal end 



Metacarpal v. is slightly shorter and more slender than mc. ii., of which 

 it forms the counterpart. The head, which articulates by a good-sized facet 



O.OI I 



Mc. iii., breadth, 



distal end . 



0.006 



.0065 



Mc. iv., length 





•0345 



•°33 



" breadth 



proximal end 



.005 



.0035 



" 



distal end . 



.0045 



.005 



Mc. v., length 





.030 



•037 



" breadth, 



proximal end 



.0035 



.005 



" 



distal end . 



.0035 



