GEOLOGICAL SURVEY OF THE TERRITORIES. 357 



described, whether recent or extinct, in the possession of canines and a 

 full series of incisors in both jaws. The genus was also hornless. 



Hyracodon nebrascensis. — The only species of the genus indicated was 

 the smallest of its American kindred, and was about the size of the little 

 hippopotamus of Liberia, Western Africa. During the miocene period 

 it existed in great numbers, associated with the R. occidentalism as proved 

 by the abundance of its remains in the mauvaises terres deposits. 

 Remains, apparently of the same species, have been discovered in Colo- 

 rado, Wyoming, and Oregon. The skull of H. nebrascensis is about ten 

 inches in length. 



HYRACHYUS. 



An extinct genus, allied to Hyracodon, is founded on a fragment of a 

 lower jaw of a young animal, obtained, during Professor Hayden's recent 

 expedition, on Black's Fork of Green River, Wyoming. In the mature 

 animal seven molar teeth formed a continuous series in the jaws. The 

 upper molars are unknown. The lower true molars resemble those of 

 Hyracodon, but the crowns have their constituent lobes more deeply sep- 

 arated externally by an angular notch. The premolars in comparison 

 with the true molars are proportionately smaller than in Hyracodon. 



Hyrachyus agrestis. — The species was smaller than Hyracodon nebras- 

 censis, and was about the size of the larger living peccary. The molar 

 series occupied a space of about three inches. The first premolar has a 

 laterally-compressed conical crown spreading in a slight posterior heel. 



Hyrachyus agrarius. — A supposed second species, probably of the 

 same genus, is inferred from the portion of a lower jaw about the size 

 and form of the corresponding part in Hyracodon nebrascensis. The 

 specimen was obtained on Smith's Fork of Green River, Wyoming. 

 The jaw below the last molar is about an inch and three-fourths deep. 

 Its ascending portion in front rises vertically, and externally is deeply 

 concave. The molar series, consisting of seven teeth, is broken away 

 in the specimen. The space occupied by the series is about three inches 

 and three-fourths. The true molars occupied a space of full two inches. 



Tapiridce. 



The existing members of the tapir family in this part of the world 

 are confined to Central and South America. During the quaternary 

 period, contemporaneously with the well-known mastodon, several spe- 

 cies of tapir inhabited North America. 



LOPHIODON. 



An extinct genus, described under the above name, by Cuvier, from 

 remains found in the middle tertiary formations of Europe, appears also 

 to have existed contemporaneously in North America. 



LopModon occidentalis. — A species, about the size of the common 

 tapir ( T. terrcstris) of South America, is indicated by a single tooth dis- 

 covered by Professor Hayden in the mauvaises terres of White River. 

 A fragment of an upper jaw, with two teeth, obtained by the Rev. 

 Thomas Condon, from Bridge Creek, Oregon, is perhaps referable to 

 the same species. 



LopModon modestus. — A small species of the same genus, thus named, 

 is indicated by a single tooth, discovered in Professor Hayden's last 

 expedition, near Fort Bridger, Wyoming. 



