Peterson: The Osteology of Promerycochcerus. 185 



tending well downwards and inwards to nearly the internal face of 

 the head of the radius, when the latter is in position. The shaft is 

 trihedral in section, the posterior border very prominent proximally 

 and gradually decreasing distad. The postero-radial border has a 

 characteristic sharp and curved ridge, which extends from near the 

 distal end upwards, one-third the length of the shaft, and overlaps 

 the shaft of the radius when the fore-arm is in position. The distal end 

 of the shaft is bent backwards and outwards giving it a sinuous curve. 

 The cuneiform facet is much expanded, slightly concave laterally, and 

 compressed antero-posteriorly with a convex surface. The pisiform 

 articulation is rather small and confined chiefly to the border near the 

 external angle. 



The Manus (Plate XXXIX, figs. 3 and 4).— The carpals are on the 

 whole very similar to those of Promerycochcerus montaniis (described by 

 Scott, /. c, p. 157-159) and only the points in which they vary from 

 that species will here be mentioned. 



The scaphoid is apparently similar to that of P. montaniis in all 

 respects, including the absence of an articular facet for the trapezium. 

 The lunar dift'ers from that of P. montanus in having no proximal 

 facet for the cuneiform. The superior portion of the bone is laterally 

 contracted, and it articulates with the radius in the usual manner, but 

 does not have proximal articular surfaces laterally for the scaphoid or 

 the cuneiform. The facet for the magnum also differs from that of 

 P. montanus, in being convex, though not as much so as in Mery- 

 cochcerus ccenopus from later deposits. Distally the bone has the 

 characteristic long beak, which nearly reaches the third metacarpal 

 and effectively separates the unciform and magnum in the anterior 

 region of the carpus (see PI. XXXIX, fig. 3). The cuneiform differs 

 from that of P. montanus, only in the absence of a proximal facet for 

 the lunar. The pisiform is rather small, with little or no neck on 

 the shaft separating the free end from the ulnar and cuneiform articu- 

 lations. The bone as a whole is relatively smaller than in Merycoido- 

 don culhertsoni. The small nodular trapezium is present and differs 

 in no respect from that of P. montanus and Mesoreodon, except in the 

 absence of a facet for Mc, II. There is no facet for a pollex. The 

 trapezoid is similar in every particular to that of P. montanus and 

 needs no further description. The only respect in which the magnum 

 differs from that of P. montanus is in the more convex articulation for 

 the lunar, a feature closely approaching what is seen in Merycocha^rus 



