1913] 



Merriam: New AncJiitheriine Horses 



421 



The teeth of no. 21056 represent an animal larger than any 

 of the known forms of Hypohippus, but approaching in size 

 Hypohippus affinis, the largest described species. They are 

 absolutely larger than the permanent premolars of II. osborni, 

 and larger than the milk molars of the type specimen of H. 

 affinis. The excess in dimensions is evident in both the antero- 

 posterior and transverse diameters. 



Comparative Measurements of Dentition 



Milk dentition 



H. nevad- 



ensis 

 No. 21056 



H. affinis 



Type 

 specimen 



28.0 ap. 



26.7 a 

 29 



Permanent dentition 



Dm 2 , anteroposterior diameter along 



outer border 33 mi 



Dm 2 , greatest transverse diameter. 29 



Dm 3 , anteroposterior diameter along 



outer border 31.8 



Dm 3 , anteroposterior diameter meas- 

 ured through protoconule and 

 hypostyle 29 



Dm 3 , greatest transverse diameter. 30.5 



Dm 4 , anteroposterior diameter along 



outer border 31.9 ap 



Dm 4 , anteroposterior diameter meas- 

 ured through protoconule and 

 hypostyle .'. 



Dm 4 , greatest transverse diameter. 31.4 



a, measurements from J. Leidy 's figure of type specimen 



b, from W. B. Scott 's figures of type specimen. 

 ap, approximate. 



H. H. 

 osborni equinus 



P 2 



27.3 



25 



P 2 



26 



25 



P 3 



25.4 



25 



P 3 



24 



22 b 



P 3 



30 



27 



P 4 



30 



25 



P 4 



25 



22 b 



P 4 



L. 



30 



26 



In form and pattern of the milk molars the Nevada specimen 

 resembles in general the permanent dentition of Hypohippus 

 osborni. The protoconule portion of the protoloph seems a little 

 more distinctly marked off from the protocone in Dm 2 than in 

 P 2 of H. osborni. In Dm 3 , however, the protoconule region of 

 no. 21056 seems less distinct than in P 3 of H. osborni. In Dm 2 

 of no. 21056 the longitudinal ridge or rib on the outer side of 

 the paracone is much less distinct and the parastyle is more 

 prominent than in P 2 of H. osborni. A small but distinct hypo- 

 style is seen on Dm 2 and Dm 3 . The size of the hypostyle is near 

 that in the premolars of H. osborni. On Dm 2 there is a strong 



