144 THE MAMMALIA OF THE DEEP RIVER BEDS. 



on the distal surface of the tibia and the sniface on the external side is much larger 

 and more deeply impressed. 



The distal end of the fibula is preserved in one specimen ; it forms a very large 

 and heavy external malleolus which is especially expanded antero-posteriorly ; on the 

 distal side is a very long facet for the calcaneum, with the outer border somewhat 

 elevated. On its inner surface the malleolus displays a projection which extends 

 beneath the facet already described on the distal aspect of the tibia. The shaft was 

 obviously reduced to the most slender proportions, though we cannot determine 

 whether it was interrupted or entire. 



The pes (PI. V, Figs. 41, 42) requires but a brief description, as it departs very 

 little from the type common to nearly all the members of the family, there being less 

 variation in the structure of the hind foot than of the front. The calcaneum has a 

 long and stout tuber, with nearly parallel borders, and thickens at the free end into 

 a heavy knob ; the fibular facet is low but very long, in which respect it differs strik- 

 ingly from that of Merycoidodon. The distal astragalar facet is very long, but, as in 

 nearly all the genera of this family, the sustentaculum projects but very little. The 

 cuboidal surface is narrow but long, measured from the dorsal to the plantar 

 edge. 



The astragalus is low and broad; the outer proximal condyle exceeds the inner 

 considerably in size, but less than in Oreodon, and is invaded by a larger sulcus ; it 

 has a more thickened and gently rounded external border than in that genus and the 

 intercondylar groove is wider and less angnlate. The navicular surface is very differ- 

 ent from that of the White River genus, extending higher up upon the anterior face 

 of the bone and having decidedly greater dorso-plantar thickness. Corresponding 

 to the structure of the calcaneum, the sustentacular surface is long, narrow, and not 

 connected with other facets. The cuboid, compared with that of the earlier genera, 

 has increased in relative height, which gives it an appearance quite like that of Mery- 

 cliyus, though it has not attained such an extreme; the calcaneal facet differs from 

 that of Meryekyua and resembles that of Oreodon in being incised lower down upon 

 the anterior face of the cuboid. The navicular has undergone no important changes, 

 unless the greater elevation of its antero-external border be so regarded; the pos- 

 terior hook is very long. The cuneiforms are very much as in the older genera. As in 

 all the members of the family, the ecto- and mesocuneiforms are coossified, the com- 

 pound bone differing from that of Merycliyus (at least of such species as M. elegans 

 and M. arenarum) in its much greater proportional transverse width. 



The metatarsals resemble those of Oreodon, but some changes may be observed 

 which point in the direction of Merycliyus. Thus, the metatarsals are straighter, less 



