South.* Dakota School of Mines 115 



from the Miocene. These are preceded elsewhere by still older 

 forms, the oldest of all so far as yet known being Protylopus 

 peter soni a little four toed creature scarcely larger than a jack- 

 rabbit, found a few years ago in the Upper Eocene beds of the 

 Washakie basin, Wyoming, and described by Mr. W. B. 

 Matthew of the American Museum- of Natural History. The 

 following are the species found in the region of the Black 

 Hills.* 



Middle Oligocene. 



Poebrotherium zvilsoni Leidy. 



Poebrotherium labiatum Cope. 



Poebrotherium eximium Hay. 



Paratylopus primaevus Matthew. 

 Upper Oligocene. 



Pseudolabis dakotensis Matthew. 

 Lower Miocene. 



Stenomylus gracilis Peterson. 



Prot ornery x halli Leidy. 



Prot ornery x cedrensis Matthew. 



Oxydactylus longipes Peterson. 



Oxydactylus brachyceps Peterson. 

 Upper Miocene. 



Procamelus occidentalis Leidy. 



Procamelus robustus Leidy. 



The commonest South Dakota species, the one first dis- 

 covered, and the one that has received the most merited 

 recognition is Poebrotherium wilsoni. The head of the animal 

 is shown in Figure 17. The collection of Big Badland 

 material given by Mr. Alexander Culbertson in 1847 to 

 the Academy of Natural Sciences of Philadelphia contained a 

 broken skull of this animal and Dr. Leidy in describing the 

 specimen, the first of the many South Dakota badland fossil 

 vertebrates studied by him, gave it the name it bears (see Figure 

 3). He first regarded the animal as allied to the musk deer but 

 later indicated its cameloid nature. Since the description of this 

 earliest Poebrotherium skull abundant other remains have been 

 found but generally they have not been complete. In 1890 the 

 Princeton expedition was fortunate in securing a very excellent 



*Later forms (Pleistocene) have been found in abundance in the Black 

 Hills region, particularly south of the South Dakota-Nebraska line, but 

 these do not come within the scope of this paper. 



