DAKOTA AND NEBRASKA. 219 



PERISSODACTTLA. 



Under this name, originally employed by Professor Owen, I distinguish an order 

 including all the uneven-toed animals of the order of Pachydermata of Cuvier, but 

 excluding the Solidungula, which are included by the former authority. Thus re- 

 stricted, the order is represented in the tertiary fauna of Dakota and Nebraska by 

 half a dozen species, mostly of extinct genera. 



The genus Lopliioclon is indicated by remains, found in association with those of 

 Hyopotamus and the much more abundant ones of Titanotherium, in the lowest 

 stratum of the Mauvaises Terres tertiary deposits of White River. The stratum, 

 marked as bed A in Dr. Hayden's tables, immediately overlies the formation of cre- 

 taceous age of the region. 



Remains of Rhinoceros, in comparative abundance, are found throughout the 

 whole series of strata of the miocene formation of White River. Those of another 

 genus of the same family — Hyracodon — are found in the same series of strata except 

 the first one, or that designated as bed A by Dr. Hayden. 



Three species of as many genera — Rhinoceros, Elephas and Mastodon — belong to the 

 pliocene formation of the Niobrara River, occupying bed F of Dr. Hayden's tables. 



Included in the account of this order there are noticed two additional species of 

 Rhinoceros, from the tertiary formations of Texas and California, and probably of 

 miocene age. 



RHINOGEROTID^. 



Among the most interesting and unexpected paljBontological discoveries in 

 America is that of the former existence of the Rhinoceros family upon this continent. 

 The remains of five distinct species have been brought to my notice from the States 

 of Dakota, Nebraska, Texas and California. Numerous remains of two of the species 

 have been collected, by different explorers, in the Mauvaises Terres of White River, 

 Dakota. These belong to the miocene formation. One of the species was probably 

 a hornless Rhinoceros of the sub-genus Aceratherium. The other has been referred 

 to a new sub-genus, with the name of Hyracodon. It was a small hornless animal, 

 provided with a full series of incisors and canines, as well as of molars. 



A third species larger than either of the preceding, distinguished under the name of 



