1898.] Wortman^ Extinct Camelidce. of North America. Ill 



region, whose treasures were destined in later years to play such 

 an important part in the development of American palaeontology. 

 Leidy at first' regarded the skull as pertaining to a genus nearly 

 allied to the Musk Deer, but later^ pointed out its true position 

 among the Camelidse. 



The generic differences between Poebrothcriiun and Protylopiis 

 are not great, and indeed it would appear at first sight that they 

 are insignificant. It is more than probable, however, as stated 



Fig. 7. Side view of skull ai Po'elnothcruiiu wi/soni. 



above, that Protylopiis will be found to have four complete and 

 functional digits in the fore limb. So far as our knowledge 

 extends at the present, the* chief distinctions are as follows : In 

 Poebrotherium the molars are much more selenoid and the crowns 

 more lengthened than in Protylopiis ; the third superior incisor 

 is larger than the superior canine ; the ulna and radius are firmly 

 coussified, even before the epiphyses of the bones are joined to 

 the shaft and the shaft of the fibula has completely disappeared. 



Poebrotherium wilsoni Leidy. 



This species, although very abundant in the White River Beds 

 of the Cheyenne River region, has not been very fully described. 

 All of the specimens in the Museum collection have been found 

 in the Lower Oreodon level, and it is doubtful if the vertical 

 range of the species extends much above this point. It differs 

 very markedly from its successor, P. labiatum, in the practical 



' "Ancient Fauna of Nebraska,' Dec, 1852, p. IQ. 



- ' Extinct Mammalian Fauna of Dakota and Nebraska,' 1869, p. 141. 



