26 



MEASUREMENTS. 



M. 



Length of skull back anterior part of Premolar 2 108 



Length of molar— premolar series, upper 045 



Length of molars, upper 0275 



Ijength of mandible 115 



Length of inferior molar premolar series 048 



Length of inferior molar series 029 



PERISSODACTYLA. 



ACHITHERIUM VON MEYER. 



In my collection from the lower Madison valley are two specimens 

 consisting of the five upper posterior cheek teeth and a mandibular 

 ramus of anotlier indiAudual. The jaw fragment containsi the symphy- 

 sis and the incisors, some of which are broken. I refer both of these 

 fragments to the same species, as they correspond in size, and there 

 IS no reason to believe that they belong to separate species. I use 

 Anchitherium in the restricted sense in which Scott has used it. The 

 Madison species thus being, so far as I know, the second found in 

 America. It is much smaller than A. aurelienense Cuv., or A. equinum 

 Scott. 



ACHITHERIUM MINIMUS, N. SP. 



This species differs from A. equinum in the following respects. In 

 iipi>er premolar 3 the cross crests are united by an isthmus across the 

 median valley, this forming two enamel lakes as in the modei*n horses. 

 This is not the case in premolar 4, and tlie anterior transverse cross- 

 crest does not reach the outer wall of the crown, but perhaps would 

 on further wear. The posterior pillar is proportionally larger than in 

 Scott's specimen. Tliere is a small pillar at the entrance of tlio 

 mediam valley in premolar 3. 



In molar 1 the median transverse cross crest is more sigmoid tlian 

 in A. equinum. The posterior pillar is connected with the hypocene. 

 It has a single enamel loop extending outward. The outer crescents 

 have rather faint median ridges, the anterior being the more prom- 

 inent. 



All the teeth are considerably worn except molar 3, in which the 

 external crescents are unworn, simple, and separated from the external 

 ones by deep valleys. The animal was much smaller than A. eguiiuin 



MEASUREMENTS. 



M. 



Lengtli of upp<^r posterior five cheek teeth 0(57 



Length of upper molar series 0415 



