44 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 128 



natural family group separate from the Hypertragulidae, A tentative 

 arrangement is as follows : 



Hypertragulidae Cope, 1879 



Hypertragulinae Matthew, 1908 



Simimeryx Stock, 1934 



Hypertragulus Cope, 1873 



Nanotragulus Lull, 1922 

 Hypisodontinae Cope, 1887 



Hypisodus Cope, 1873 

 Leptomerycidae Scott, 1899 



Leptotragulinae Zittel, 1893 



Leptotragnlus Scott and Osborn, 1887 



Leptorcodon Wortman, 1898 



Poabromylus? Peterson, 193 1 

 Leptomerycinae Zittel, 1893 



Leptomeryx Leidy, 1853 



Heteromeryx Matthew, 1905 



This does not, however, take into account the Protoceratidae. 

 Scott (1899) was of the opinion that Protoceras was derived from 

 Leptoreodon. However, he considered that Stiharus may have been 

 a connecting link. There is much to be said in favor of an interpreta- 

 tion that places the leptotragulids in an ancestral position to Proto- 

 ceras, but this does not include Stiharus, and the Uintan stage is much 

 better represented by Leptotragulus as far as the dentition is con- 

 cerned. This is most interestingly displayed by the lower premolars. 

 There is little to distinguish the leptomerycids, leptotragulids, and 

 protoceratids in the molar structures, but they may be diagnosed by 

 their premolars, and among these the two that are most alike in this 

 respect are Protoceras and Leptotragulus. The various protoceratids 

 form a natural family group that would be obscured in the Lepto- 

 tragulinae, and removing Leptotragulus from Leptoreodon, as an 

 association of primitive and related leptomerycids, tends also to 

 distort the picture. A suggested arrangement is shown in the phylo- 

 genetic chart. 



Genus SIMIMERYX Stock, 1934 



Type. — Simimeryx hudsoni Stock, 1934. 



Discussion. — Stock's description of this form and estimate of its 

 probable relationships appear quite accurate. The resemblance to 

 Hypertragulus is rather close and particularly striking in characters 

 of the premolars, both upper and lower. With these teeth the principal 

 differences to be noted are the somewhat less reduced size anteriorly, 

 the absence of a diastema between P2 and P3, the less-selenodont 



