Vol. 5] Gidley. — Fossil Mammals from Virgin Valley. 241 



types of horses, are of especial interest since they suggest oppo- 

 site lines of development, of the hind feet, from an intermediate 

 type such as that of Mesohippus. The first astragalus (see figs. 

 4 and 5) is short and broad with widely open tibial groove, and 

 well rounded keels. The inner keel is not deflected at its distal 

 extremity as in Mesohippus, but terminates in direct line with 

 its oblique fore and aft plane. The second (figs. 6 and 7) is 

 more elongate, the keels much compressed laterally, and the tibial 

 groove much narrower and more angulate in cross-section. The 

 inner keel is deflected at its distal extremity as in Mesohippus, 

 and even to a greater degree than in that genus. The first of these 

 astragali is characteristic of the comparatively short, broad foot 

 of the Hypohippus type, and is probably referable to a species of 

 that genus. The second is of uncertain reference, but indicates 

 a more highly specialized foot of the long and slender type like 

 that of N eohipparion whitneyi or some of the more specialized 

 forms of feet belonging to species of the Parahippus group. In 

 its more important characters the Mesohippus astragalus is in- 

 termediate between these two forms. 



The last specimens of importance to be considered in this little 

 collection from the Virgin Valley locality are two isolated teeth 

 which are referable to Palaeomeryx, as that genus is at present 



Figs. 8 and 9. — Palaeomeryx? borealis (Cope). Last upper molar, no. 10G76, 

 natural size. 



understood. The more characteristic tooth (no. 10676) is a 

 portion of a last upper molar of the right side, with the inner 

 walls of the protocone and hypocone broken away. The crown is 

 short, brachyodont, with well developed external styles and well 

 marked external ribs. It agrees very nearly in size with the 



PALAEOMERYX? BOREALIS (Cope). 

 Figs. 8 and 9. 



8 



9 



