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io 5 



UINTA SELENODONTS 



The sustentacular facet is very broad proportionately, a point of resemblance 

 to the White River genus, though its internal border is not so much elevated ; 

 the external calcaneal facet is more oblique and more deeply concave than in 

 the latter, and the fibular facet somewhat broader. Though the distal trochlea 

 is missing, yet the surfaces for it upon the cuboid and navicular show that the 

 facet for the former was relatively broader than in Protorcodon, approaching 

 the proportions seen in Agriochcenis. 



Very little of the calcaneum is preserved, only the distal end with the 

 fibular facet ; this end has upon its external side a broad, deep sulcus, such as 

 is found in Agriochcenis, but not in Protoreodon. The cuboidal facet is no 

 broader — indeed, is relatively narrower — than in the latter, but has a consider- 

 ably greater dorso-plantar diameter, and the distal astragalar surface is like- 

 wise more extended in the same direction. The fibular facet is narrower and 

 rises higher and more abruptly than in Agriochcerus and is more regularly 

 arched, while the proximal astragalar facet is more oblique and forms a sharp 

 ridge by its junction with the fibular surface. The sustentaculum is badly 

 broken, but the corresponding facet upon the astragalus shows that it must 

 have projected more prominently than in Protorcodon. Between Agriochcenis 

 and Oreodon we find similar differences ; in the latter, as in all the oreodonts, 

 the sustentaculum projects but very little from the tibial side of the calcaneum, 

 while in Agriochcenis it is much more prominent. 



The cuboid is decidedly lower and broader proportionately than in Pro- 

 toreodon, though it has not yet become so low, wide, and thick as is the case 

 in Agriochcenis. The difference in this respect between Protagriochcerus and 

 Protoreodon is much the same as that between their White River successors, 

 in both of which the tarsal bones have shortened and broadened, but far more 

 so in Agriochcerus than in Oreodon. The calcaneal facet is quite broad, though 

 hardly so wide proportionately as in Protorcodon ; it is also less steeply in- 

 clined than in the latter, but descends farther upon the dorsal face of the bone. 

 The astragalar facet is broader proportionately than in Protoreodon and of 

 nearly the same relative size as in Agriochcerus, but its dorsal border rises 

 higher proximally. On the tibial side of the cuboid are three facets for the 

 navicular, a large concavity on the plantar border, and on the dorsal margin two 

 small plane facets separated by a deep groove. Of these dorsal facets the distal 

 one is carried upon a prominence, which also bears a facet for the ecto-cunei- 

 form. In Agriochcerus the plantar facet for the navicular is much the same as 

 in the Uinta genus, but on the dorsal side is only a single facet for the navicular 



