FREE INSTITUTE OF SCIENCE 

 UINTA SELENODONTS 



Of the fibula only the distal half is preserved in the most complete speci- 

 men, but that displays some interesting' transitional characters. In Poebro- 

 therium only the ends of the bone are retained, the proximal end as a short 

 spine anchylosed with the tibia and the distal end as a malleolar bone. In the 

 Uinta genus, except, perhaps, in aged individuals, there is no anchylosis, and 

 the shaft, though reduced to a mere thread of bone, was apparently complete. 

 At all events, fully half of its length is present in the specimen before us, and 

 from the appearance of the tibia I should infer that it was uninterrupted. 

 The filiform shaft is closely applied to the tibia and its distal portion expands 

 considerably in the dorso-plantar dimension, though remaining extremely 

 narrow. The distal end forms a stout malleolus, which is partly overlapped 

 by the tibia; its facet for the calcaneum is narrow and almost plane. 



The pes (Plate II., fig. 8) has more nearly attained the condition found in 

 Poebrotlicriwn than has the manus, though certain more primitive features 

 are still to be found. The tarsus is high and narrow, higher and narrower 

 than in the White River genus, but with similar elements arranged in a 

 similar way. A small bone, probably the tibiale, is attached to the tibial side 

 of the astragalus. 



The astragalus, like the whole tarsus, is high and narrow ; its proximal 

 trochlea is deeply and narrowly grooved and is quite asymmetrical, the exter- 

 nal condyle exceeding the internal somewhat in height and very considerably 

 in breadth. The sustentacular facet is rather narrow and short, and occupies 

 an oblique position. The distal surface has a narrow facet for the cuboid 

 and a broad, hour-glass shaped facet for the navicular. In Poebrothcriinn a 

 few changes in the character of the astragalus may be noted ; its proximal 

 trochlea is more broadly grooved, and in the distal trochlea the cuboidal facet 

 has become relatively wider. 



The calcaneum is quite elongate and has a slender tuber; it is remark- 

 able for the broad and deep depression which runs for nearly the entire length 

 of the bone, broadening and deepening distally. On the plantar border the 

 calcaneum is nearly straight, except that the distal end of this border rises 

 steeply towards the cuboidal facet. The dorsal border of the tuber rises grad- 

 ually to the fibular facet, which forms a prominent convexity, rising steeply 

 on both proximal and distal sides. The cuboidal facet is narrow and so 

 warped that its plantar portion presents inward as well as distally. The sus- 

 tentaculum is of only moderate prominence and bears a simply concave facet ; 

 it is separated from the tuber by a deep sulcus, which runs for a short distance' 



