'J2 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. I44 



although the foot bones, of denser material, have retained much of 

 their original shape. The skeletal portions closely resemble those in 

 Bridger Uintatherium. The limb bones, though about two-thirds the 

 length of those in an upper Bridger animal, are relatively much more 

 slender. In comparison with the skeletal material Dorr (1958) has 

 called Prottintatherium, I note that the groove between the inner and 

 outer or trochlear and capitellar portions of the distal articular surface 

 of the humerus is more obtuse, approaching Uintatherium in this 

 respect. Also, the olecrenon of the ulna curves backward more and 

 the sigmoid notch faces more proximally, as in Uintatherium. 



The astragalus figured by Dorr belongs to Coryphodon, as he sus- 

 pected. The New Fork astragalus is much like that in Uintatherium 

 but shows a somewhat less flattened surface for the tibia, and that 

 for the cuboid and navicular is relatively a little deeper in a dorso- 

 plantar direction and not so wide. The latter surface, moreover, is 

 sharply tilted with respect to the tibial surface and they approach one 

 another at a high angle. In Uintatherium these surfaces of the as- 

 tragalus are more nearly opposite one another. This suggests greater 

 forward tilting of the tibia with respect to the metatarsal direction. 

 An additional feature noted is that an astragalar foramen is not en- 

 closed or completed in the New Fork am'mal, whereas formation of 

 the foramen seems characteristic of the Bridger animal, 



PERISSODACTYLA 

 EQUIDAE 



HYRACOTHERIUM, cf. ANGUSTIDENS (Cope) 

 (Plate 13, figure 3) 



In assigning the Bitter Creek material of Hyracotherium tenta- 

 tively to H. angustidens, I have followed Kitts in his belief that the 

 materials from Graybullian beds in both New Mexico and Wyoming 

 represent a definably more primitive stage in this genus than the later 

 Wasatchian specimens. This is without regard for the rather striking 

 range in size observed. Some teeth are as large as any referred to 

 H. vasacciense in the La Barge collection and others are smaller than 

 any that I had previously referred to H. index. No statistical treat- 

 ment of this material seemed feasible, as all but about four specimens 

 of the approximately three dozen consist of isolated teeth from 

 various positions. 



Three of the isolated teeth are believed to be P^, as determined from 

 their somewhat less transverse diameter in comparison with their 



