Cope.] *>"^ [Oct. 7, 



Hyperlragulus must be associated with Dorcatlierium on account of 

 the lack of cannon bone. Lophiomeryx has an inferior type of inferior 

 true molar, and like Dorcatlierium has four toes on all the feet. Hyper- 

 lragulus displays greater specialization in the absence of lateral digits from 

 the posterior feet. The ulna is also coossified with the radius, and there 

 is a naviculocuboid bone. The premolar teeth are nevertheless very sim- 

 ple, and are separated by diastemata in both jaws. It must be regarded 

 as a modified descendant of Dorcatlierium on one side of the main line of 

 descent. 



In the next group the metatarsals have united while the metacarpals re- 

 main separate. This is the case in Leptomeryx of the American Oligo- 

 cene. In Tragulus the premolars are much simpler than those of the 

 other genera of Section III, and simpler than those of Leptomeryx, so that 

 these two forms must have been derived from an ancestor which combined 

 the simplicity of both forms. For this we must again recur to Dorcathe. 

 rium, and I therefore insert this genus at the base of the following dia- 

 gram. With its entirely prismatic molars Hypisodus has one element of 

 superiority, but the number of its superior premolars is unknown. 



Prodremotherium Bachitherium 



y 



Amphitragulus Gelocus 



\ 

 \ 



Tragulus Leptomeryx 



/ Hypertragulus 



Dorcatherium 



I 

 Lophiomeryx 



Of the PoEBROTHERiiD^ there are two genera. These differ as fol- 

 lows : 

 First premolar of upper jaw elongate and with two roots 



Poebr other ium Leidy. 

 First upper premolar short and with a simple conic root 



GompJiotJierium Cope. 



The phylogenetic relations of these genera correspond with their rela- 

 tive geological positions. In Gomphotherium from the John Day (Mid- 

 dle) Miocene, the first premolar is much reduced, probably soon to be 

 aborted, as is the case in later genera of the line, among the Camelidte. 

 In Poebrotherium it displays an unusual development, like that of some 

 Tragulida3. 



With the Poebrotheriidse we commence a series of families characterized 

 by the absence of the vertebrarterial canal, or the line of the camels 

 proper. 



