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79 



UINTA SELENODONTS 



with the unciform, is slightly enlarged and thickened; this is principally due 

 to the tubercle for the insertion of the extensor carpi ulnaris muscle. The 

 shaft is slender, laterally compressed, and almost straight, though displaying 

 a slight lateral curvature. 



No phalanges have been found in connection with the manus. 



Of the tarsus (Plate III., fig. 18) only the astragalus, calcaneum, and 

 cuboid are preserved, but these are sufficient for a satisfactory comparison 

 with the tarsus of the other Uinta genera. The astragalus is very much like 

 that of Protylopus, though a little smaller in actual size and somewhat broader 

 and shorter proportionately. The proximal trochlea is very asymmetrical, the 

 external condyle exceeding the internal even more than in Protylopus, while 

 the deep intercondylar groove is somewhat broader and more open than in 

 that genus. Both of these condyles, and especially the inner one, are rather 

 more widely separated from the distal facets for the cuboid and navicular re- 

 spectively. The various facets for the calcaneum, so far as they can be made 

 out, do not differ in any important respect from those on the astragalus of Pro- 

 tylopus, save that the surface for the sustentaculum appears to be hardly so 

 wide in proportion. The distal trochlea is very unequally divided between the 

 facets for the cuboid and navicular ; the relative breadth of the two facets is 

 about as in Protylopus, but that for the navicular is of different shape, in that its 

 convex portion is rather narrower. The whole distal trochlea lies somewhat 

 internal to the proximal one, and this gives an oblique shape to the entire 

 bone. In Leptomeryx the astragalus is suggestively like that of Camelomcryx, 

 but exhibits a number of advances. Owing to the increased size of the in- 

 ternal condyle, the proximal trochlea is less asymmetrical and the intercon- 

 dylar groove is wider ; the shape of the bone is less oblique, the proximal and 

 distal trochlear being more nearly in line, and the cuboidal facet is distinctly 

 broader, while the dorso-plantar diameter of the whole bone is increased. 

 Leptoreodon has an astragalus almost exactly like that of Camelomcryx, but is 

 a little longer and narrower, and the distal trochlea has a somewhat different 

 shape, due to the shallowness of the concave portion of the navicular facet. 

 In Protoreodou the astragalus is of the same general type, but is heavier and 

 more oblique in shape, with more asymmetrical proximal trochlea and more 

 rounded angles. 



The calcaneum is a rather small and slender bone, with perhaps a 

 greater resemblance to that of Leptomeryx than to the corresponding tarsal 

 in the other genera which have been mentioned. The tuber calcis is quite 



