96 The Badland Formations of the Black Hills Region 



Middle Oligocene. 



Mesohippus bairdi Leidy. 

 Mesohippus obliquidens Osborn. 



Upper Oligocene. 



Mesohippus intermedins Osborn and Wortman. 

 Mesohippus meteulophus Osborn. 

 Mesohippus br achy stylus Osborn. 

 Miohippus validus Osborn. 

 Miohippus gidleyi Osborn. 

 Miohippus crassicuspis Osborn. 



Lower Miocene. 



Parahippus crenidens Scott. 

 Parahippus nebrascensis Peterson. 

 Parahippus tyleri Loomis. 



Upper Miocene. 



Hypohippus affinis Leidy. 

 Protohippus pcrditns Leidy. 

 Protohippus placidus Leidy. 

 Protohippus sup remits Leidy. 

 Protohippus pernix (Marsh). 

 Protohippus simus Gidley. 

 Neohipparion whitneyi Gidley. 

 Neohipparion occidentale (Leidy). 

 Neohipparion dolichops Gidley. 



Of the above named species the commonest and most noted 

 one is Mesohippus bairdi of the Middle Oligocene (see Plate 

 32). Prof. Leidy first described this in 1850 as Palaeotherium 

 bairdi, but later changed the name to Anchitherium bairdi. Prof. 

 Marsh in 1875 erected it into the type of a new genus, Meso- 

 hippus, hence the present name. In consequence of the fact that 

 all of the earlier skeletons found were much broken and poorly 

 preserved, and only the best bones saved, for forty years little 

 was known of the animal except what could be learned from the 

 foot bones and the head. Since 1890 several well preserved, 

 nearly complete skeletons have been found and some of these 

 have been described in much detail.* 



*See especially thiei following: 



Scott, W. B. On the Osteology of Mesoihiippus and Leptomeryx, 

 with Observationis on the Modes and Factor© of Evolution in the 

 Mammalia. Journ. Morph., Vol. 5, 1891, p>p. 301-406. 



Farr, M. iS. Notes on the Osteology of the White River Horses. 

 Proc. Am. Philos. SOc, Vol 35, 1896, pp. 147-175. 



