2.51 



The tootli i.s devoid of" eoinentuni, and resembles in its constitution the cor- 

 responding one of Anchitherium nearer than it does that of other known 

 equine animals. The inner and intermediate lol)es appear somewhat fuller 

 than in Anchitherium, and the intermediate spaces narrower and less con- 

 vergent at bottom. 



It maj' perhaps belong to Anchippus, founded on an imperfect tooth from 

 the same locality, and represented in Fig. 13, Plate XXI, of the Extinct 

 Mammalian Fauna of Dakota, &c. It presents important peculiarities, l)ut 

 these may depend on the difierence of position of the tooth in the series. 

 There is, however, one feature in the tooth of Anchippus which is absent in 

 the specimen under consideration, rendering it probable that the teeth per- 

 tain to different genera: The feature to which I allude consists of a con- 

 spicuous fold or offset from the postero-median lobe projecting into the oljlique 

 valley of the crown toward the antero-median fold. In Parahippus the same 

 fold exists in a more complex condition. 



The tooth in question likewise resembles that represented in Fig. 11, Plate 

 XXI, of the work above quoted, as characteristic of the genus Hypohippus, 

 nearly as much as it does those of Anchitherium, and may, perhaps, belong 

 to a smaller species of the former. 



In the uncertainty as to the nearer generic relationship of the specimen it 

 may be regarded as indicative of a species of Anchitherium with the name 

 given at the head of the chapter. Tiie species was about as large as the 

 Anchitherium aurelianense of the Eocene Tertiary deposits of France. 



The estimated size of the tooth is 11 lines in diameter antero-posteriorly 

 and nearly the same measurement transversely. 



Anchitherium agreste. 



During Professor Hayden's exploration in Montana, he discovered several 

 fossil jaw-fragments of a species of Anchitherium. They were found in asso- 

 ciation with a Helix, partially imbedded in an indurated, gray, arenaceous 

 marl, and were derived from a lacustrine Tertiary deposit on Red Rock 

 Creek, one of the head Ijranches of the Jefferson Fork of the Missouri 

 River. 



The jaw-specimens belonged to a species considerably larger than the 

 Anchitherium Bairdi of the Miocene Tertiary of White River, Dakota, and 

 approached in size (lu,^ A. aurelianense of the Pliocene Tertiary of France. 



