THE MAMMALIA OF THE DEEP EIVER BEDS. 179 



Camelidae. 



POEBROTHERIUM Leidy. 



Proc. Acad. Nat. Sci. Phila., 1847, p. 322. 



The lower beds yielded a number of more or less fragmentary remains of this 

 genus, the teeth showing perhaps a stronger tendency to assume the prismatic form 

 than do the earlier species from the White River and Oregon beds. 



PROTOLABIS Cope. 



Proa. Acad. Nat. Sci. Phila., XXVIII, p. 145. 



From the upper beds were obtained several specimens of small camels which 

 should probably be referred to this genus. Only one of these is worthy of more than 

 passing notice. This specimen is an axis (PL VI, Figs. 52, 53) which is of interest 

 as demonstrating the mode of development of the spout-shaped odontoid in the 

 camels. I have elsewhere shown that while Procamelus has a spout-like odontoid 

 quite similar to that of the existing tylopodans, the White River Poebrotherium has 

 a fiat or semiconical process. In the specimen before us the margins have become 

 slightly elevated, giving the process a somewhat concave upper surface and repre- 

 senting the same stage as that shown by the John Day genus, Miolvippus, among 

 the horses. So far as the odontoid process is concerned, the horses and camels thus 

 form exactly parallel series, though all the steps of the change did not occur contem- 

 poraneously in both lines. 



PROCAMELUS Leidy. 



Proc. Acad. Nat. Sci. Phila., 1858, p. 89. 



This genus is represented by a number of fragmentary specimens from the 

 upper beds, but they add nothing whatever to our knowledge of the genus. 



PEOBOSCIDEA. 



Mastodon proavus Cope. 



Synopsis of New Vertebrata from the Tertiary of Colorado, 1873, p. 10. 



Some vertebras and fragments of limb bones, which doubtless belong to this 

 species, confirm Cope's statement that this is the oldest horizon containing Mastodon 

 which has yet been found in America. The bones were found in position only in the 

 uppermost beds, but loose fragments were found in the middle of the upper series. 

 Except stratigraphically, these specimens are of no especial interest. 



