426 University of California Publications in Geology [Vol. 7 



lateral digits and their ungual phalanges are relatively large, 

 and were evidently functional. The first and second phlanges of 

 the median digit are relatively shorter and wider than in the 

 Merychippus forms of the Miocene. The ungual phalanx of the 

 median digit is broad, and the lateral wings show a stage of 

 development at least as advanced as in Hypohippus. Metacarpal 

 three shows a distinctly oblique lateral facet for articulation 

 with the unciform. In metatarsal three there seems to be a very 

 small and quite oblique facet for the cuboid. In general the 

 limb structure resembles that of Hypoliippus. 



Measurements of Limb Elements 



Radius, greatest length of shaft 241 mm. 



Radius, least width of shaft 25 



Metacarpal II, greatest length 190 



Metacarpal III, greatest length 192 



Metacarpal III, width of distal end, approximate 28.5 



Phalanx I, digit III of anterior extremity, greatest length 40 



Phalanx 1, digit III of anterior extremity, greatest width 30 



Phalanx II, digit III of anterior extremity, greatest length...... 30 



Phalanx II, digit HI of anterior extremity, greatest width 31 



Metatarsal III, greatest length 203. 



Metatarsal IV, greatest width at proximal end 17 



Phalanx I, lateral digit (hind foot?) greatest length along- 

 superior side 23.5 



Phalanx III, lateral digit (hind foot?) length along superior 

 side 35 



Relationships. — The form represented by the Nevada speci- 

 men, no. 21056, resembles Hypohippus in the characters ' of the 

 limbs and in the general form of the cheek-teeth. It differs from 

 Hypohippus in the separation of metaloph and ectoloph in the 

 milk dentition. It is uncertain whether the permanent dentition 

 of this species is represented in any of the collections from the 

 Great Basin region. A difference in tooth characters comparable 

 to that separating this species from typical Hypohippus is 

 ordinarily considered as of generic value. In this particular 

 case, the total characters, so far as known, indicate that the 

 species is much nearer to Hypoliippus than to any other group, 

 and excepting the separation of metaloph and ectoloph is not 



