160 THE MAMMALIA OF THE DEEP RIVER BEDS. 



shorter than the second and is heavier, especially towards the distal end ; the facet 

 for mc. iv is oblique in position. While the median metacarpals are closely applied 

 to and run parallel with each other, the lateral ones, mc. ii and mc. v, diverge quite 

 strongly from the median axis, and thus give a foot with a very broad base. 



The phalanges are short, broad, much depressed and flattened. Unguals are not 

 preserved in any of the specimens. 



Except for its increase in size and weight, the femur differs but little from that 

 of the older genera of the family. Compared with the femur of JSjJoi'eodon, the fol- 

 lowing changes may be observed. The head is rather more sessile and projects more 

 upward and forward and the pit for the round ligament is larger and deeper. The 

 neck is less constricted and the bridge connecting the head with the great trochanter 

 is thicker and more rugose. The great trochanter, though massive and extended 

 antero-posteiiorly, is rather low, not rising so high as the head; it encloses a very 

 deep digital fossa. The second trochanter is smaller and less prominent. The shaft 

 is broader and less rounded and the medullary cavity is larger, with thinner walls. 

 The deep pit above the external condyle for the origin of the plantaris muscle is 

 more conspicuously marked. As in the John Day genus, the condyles are of nearly 

 equal size and are separated by a wide and deep groove. The rotular trochlea is 

 somewhat more modernized, being wider and less symmetrical; the external border 

 is more prominent and continued farther distally than the internal. 



The proximal end of the tibia is not known. The distal end is very heavy; the 

 external fossa for the astragalus is considerably broader and less deeply incised than 

 the internal one, and the malleolar process is remarkably long and heavy; on the 

 external side is a small concave facet for the fibula. The fibula has a shaft which is 

 very large in the antero-posterior dimension, though very thin and compressed lat- 

 erally. In the upper Loup Fork species, 31. ccenojnts, the shaft is much more slender 

 and reduced to almost thread-like proportions. The distal end is expanded into a 

 very heavy external malleolus, which, like the shaft, has its greatest diameter antero- 

 posteriorly. On the inner side is a projection which fits into a groove on the tibia, and 

 distal to this is a large plane surface for the astragalus, which does not, however, 

 occupy all of the tibial side of the malleolus. The calcaneal facet is narrow and 

 slightly concave transversely, but extended in the fore-and-aft direction. 



The tarsus is lower and broader and the individual elements more massive than 

 in the earlier genera of the Oreodontidce, but otherwise there is little change. The 

 astragalus is low and broad; the external proximal condyle is considerably larger 

 than the interna], but the difference is less extreme and the intercondylar groove is 

 narrower and deeper than in 31. ccenopus. On the distal trochlea the navicular sur- 



