Peterson: Material Discovered in Uinta Basin. 133 



The humerus is laterally compressed proximally, which is in part 

 due to crushing. The greater tuberosity rises considerably above 

 the head. There is a large deltoid groove and the deltoid ridge is 

 prominent, but does not have the large and rugose tuberosity seen in 

 Ilyracodon, and the supinator ridge is also less developed. The distal 

 trochlea is relatively slightly narrower than in the latter genus, but 

 resembles it closely in height, its very prominent and narrow inter- 

 condylar ridge, and narrow outer condyle (PI. XLVT, Fig. 4). 



The radius is only very slightly longer than the humerus, and in 

 'this respect is quite similar to the same bone in Hyracodon, though 

 slenderer. Its head is not greatly expanded and the shaft is broad 

 and rather compressed antero-posteriorly, with a considerable bow 

 in the same direction, while distally it is expanded both laterally and 

 antero-posteriorly, with deeply excavated facets for the scaphoid 

 and the lunar. The shaft of the ulna is more reduced than in Hyra- 

 codon of the Oligocene, but, as in that genus, it is at no place coossified 

 with the radius. 



The carpus agrees with the description given by Osborn (/. c, 

 pp. 527, 547) except the trapezium, which according to Osborn is 

 greatly reduced. This is probably a mistake, since the trapezium of 

 one individual (No. 2336) of the Carnegie Museum is of considerable 

 size, and the large facet on the radial palmar angle of the trapezoid 

 of the specimen under description indicates a bone proportionally 

 quite as large as in Hyracodon. 



The metacarpals are all complete, and plainly show that they are 

 much shorter proportionally than in Mesohippus, the genus with 

 which Professor Osborn compared the pes of Triplopus. Mc. I is 

 entirely absent, Mc. II and IV are reduced in size, but not quite as 

 much as in Hyracodon, \n\\\\q their length in comparison with Mc. Ill 

 is fully as much or even more reduced than in that genus. Mc. V 

 is reduced to about the same extent as in Hyracodon (See Plate XLVI, 

 Fig. 2). 



The median phalanx of the proximal row is broad and depressed, 

 while those of the lateral digits are higher. The ungual phalanges 

 are also depressed, somewhat pointed and cleft, suggesting the features 

 of the early horses to a remarkable degree. 



With No. 3199, already referred to above, there is unfortunately 

 only preserved a fragment of the pelvis, the femur, and the metatarsals, 

 while the entire length of the tibia, except the epiphysis of the prox- 

 imal end, and the greater portion of the tarsus is present. 



