THE MAMMALIA OF I'llE UINTA FOUMATIOX, 547 



Carpus. In tlie tetradactyl Huraclujus we find nil the distinctive features of 

 the carpus in tliis series are practically attained, these resulting from the great lateral 

 displacement. The scaphoid has a very narrow trapezium facet and broad and 

 decidedly oblique trapezoid facet; it rests broadly upon the maijnura. In the 

 lunar the radial facet is shallow; it is compressed below, with a narrow oblique 

 anterior facet ujaon the magnum and broad subhorizontal unciform facet. The 

 scaphoid and lunar thus rest principally upon the magnum and unciform. The cune- 

 iform presents a small ulnar facet, this bone being rather slender. The trapezoid has 

 a broad trapezium facet. The magnum has a narrow and oblique lunar facet. The 

 unciform is a very characteristic bone since its vertical is greater ihau its transverse 

 diameter. It nevertheless has a narrow facet for mc. v, which, according to Cope, is 

 considerably the most slender. 



Taken altogether the vertical and transverse diameter of the carpus is aV)out the 

 same. 



In I'rijtlojnts the vertical diameter of the cari)us is slightly greater than the 

 transverse, the metapodials and carpals are somewhat rolled backwards so that the 

 anterior face of the manus is sti'ongly convex. Every feature in which the manus 

 departs from that of ILjrachyus is in the direction of greater elongation and lateral 

 displacement. The scaphoid is narrow and has a very oblique trapezoid facet ; 

 its main weight descends upon the magnum. (The small trapezium and the trapezoid 

 are missing in the Princeton collection.) The 1 u n a r rests entirely upon the unciform, 

 its contact with the magnum anterioi'ly is by a vertical facet, variable, never in the 

 nature of support, sometimes entirely wanting. The c u n e i f o r m, like the scajihoid, 

 is rotated backwards. Judging by the facets upon the mc. ir and the scaphoid, the 

 trapezoid was laterally compressed. The vertical diameter of the unciform exceeds 

 the transverse ; it still bears a considerable mc. v facet. 



Ill I lijracodon, the carpus repeats the structure of TriphjjH/s upon a larger scale. 

 The proportions of the metapodials are approximately the same ; the proximal por- 

 tion of mc. V persists but is very much reduced in size. The magn u m lias ivl.i- 

 tively increased in size, but still has a very limited contact with the lunar anteriorly. 

 The trapezium is small and has no contact with mc. n. The vertical diameter of 

 the unciform much exceeds the transverse; the cuneilbrm is also high and vei-y nar- 

 row. The degree of backward rotation of the lateral elements evidently varies in 

 the different species. 



Taiwus. In the astragalo-cuboidal articulation, ill the niimluT and disposition 

 of the digits and in the shape of the terminal phalanges, this series closely' approaches 

 the equine series, and. in some eases, can be distinguished onl}' by very careful 



