468 Bulletin American Muscujn of Natural History. [Vol. XIX, 



strongly developed as in Eqiius cahalliis and here is no trace 

 of the external median ribs of the meta- and paracones. 

 These last two characters are apparently common to all the 

 species of Neohipparion and may be of generic importance. 



Though the teeth in the present specimen are worn just to 

 the stage when they present the most complicated pattern of 

 enamel folding, they are very simple in this respect. 



The Lower Jaiv. — The incisors, like those of the upper jaw, 

 are only moderately long-crowned, and are all fully cupped. 

 The external pair is smaller than the others. The first pre- 

 molar (pi) is entirely wanting. The molars and premolars 

 show an advanced stage of progression in the greatly flattened 

 external walls of the para- and hypoconids. The antero- 

 external enamel fold of the protoconid, except in pa, is 

 strongly developed. The lower border of the jaw is very 

 much curved. 



The Milk Dentition. — There is no trace of p' in the milk 

 series of one of the specimens, but another associated speci- 

 men possesses this tooth reduced to a mere vestige. In the 

 upper molars the protocones are strongly developed and free 

 as in the adult. They are elongated in cross-section, though 

 not to the degree shown in the permanent series. The lower 

 molars possess a little tubercle arising from the cingulum be- 

 tween the para- and hypoconids. This conule is much 

 shorter than in the Hipparion of Europe, but broader antero- 

 posteriorly, being elliptical in cross-section. The outer walls 

 of the para- and hypoconules are flattened, but in less degree 

 than in the permanent series. 



II. The Skull. 



There are many primitive characters observable in the 

 skull, the most jDrominent of which are the vertical thickness, 

 general shortness, and consequently the relatively large space 

 occupied by the molar-premolar series. The orbit is placed 

 well forward, its anterior border being above the posterior 

 half of p'^. The anterior projection of the masseter ridge 

 extends forward to the middle of m'. The position of the 

 infraorbital foramen is between p^ and p*. The facial pit is 



