THE MAMMALIA OF THE DEEP KIVER BEDS. 



1G1 



face is wider and the cuboidal narrower than in the last named species. The 

 calcaneum is short and massive and is remarkable for the sessile character of the 

 sustentaculum; in the other members of the Oreodontidm the sustentaculum projects 

 but very little beyond the tuber, though in none of them, except Merychyus, is this 

 so marked as in Merycochoerus. The fibular facet is elongate antero-posteriorly, 

 narrow and arched. The navicular is relatively wider than in M. ccenojms, but is so 

 nearly like that of the older well-known genera as to require no detailed description. 

 The cuboid is low and broad and differs from that of Oreodon in the relative width 

 of the proximal facets, the astragalar being wider than the calcaneal, while in the 

 White River genus the calcaneal is the broader. The difference in M. montanus is 

 not, however, so marked as in the species from the upper Loup Fork. The calcaneal 

 facet is not only narrower than in Oreodon but of different shape, the external border 

 being straight and not projecting beyond the body of the bone. The facet for the 

 astragalus is not so deeply concave as in the more ancient genera of the family, the 

 dorsal and plantar margins not rising so high. On the tibial side are two facets for 

 the navicular, which are separated by a deeper sulcus than in Oreodon. The distal 

 side is almost completely taken up by the large facet for the fourth metatarsal ; that 

 for mt. v is very small and rather lateral than distal, while in Oreodon it is altogether 

 distal. The posterior hook of the cuboid is very massive. 



The entocuneiform is quite a large nodular bone, which articulates with the 

 navicular and mesocuneiform and abuts against the plantar side of the head of the 

 second metatarsal, which it holds firmly in place. As in all the known members of 

 the Oreodontidce, the meso- and eetocuneiforms are coossified, and, since the former 

 has less vertical height than the latter, the compound bone appears to have a step 

 cut in its distal side, which receives the head of the second metatarsal and prevents 

 the third from reaching the mesocuneiform. 



The metatarsus departs less from the family type than does the metacarpus, both 

 in its proportions and in its mode of articulation with the podials. The median 

 metatarsals are, however, relatively shorter and more massive and the laterals more 

 reduced than in the more ancient genera. The slenderness of the laterals and their 

 parallelism with the medials are in striking contrast to the lateral metacarpals, which, 

 though shorter than the median pair, are nearly as heavy, and which diverge strongly 

 from the axis of the manus. The second metatarsal is not only proportionately, but 

 even actually, shorter than in the much smaller Oreodon Culbertsoni, and is the shortest 

 of the series. The head articulates with all three of the cuneiforms ; on the posterior 

 side is a facet for the entocuneiform, the proximal end is supported by the mesocu- 

 neiform, and since the latter is of less height than the ectocuneiform, the fibular side 



