24 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 128 



much as in Microsus and Homacodon, and rather like Protodichobune 

 as well. Hexacodus, and hence Antiacodon, are regarded as homaco- 

 donts but in a sequence somewhat divergent. Although the end 

 product, Antiacodon, would appear to be significantly different and 

 markedly divergent from Microsus and Homacodon, I have not felt 

 that full subfamily recognition was justified, particularly since Hexa- 

 codus so closely resembles Microsus. 



The remaining known genera of homacodonts, i.e., Bunomeryx, 

 Hylomeryx, Sphenomeryx, Mesomeryx, and Pentacemylus, are all 

 peculiar to the upper Eocene and herein discussed at greater length. 

 One of these, Sphenomeryx, is regarded as a synonym of Hylomeryx, 

 and the new genus, Mytonomeryx, is described. Remains representing 

 species of these have been found so far only in the Uinta formation, 

 except for Pentacemylus progressus Peterson, which was originally 

 named from a Duchesne River specimen. Pentacemylus is now much 

 better represented by Uinta C material. 



Genus BUNOMERYX Wortman, 1898 



Type. — Bunomeryx montanus Wortman, 189S. 



Discussion. — The genus Bunomeryx was described by Wortman 

 as a part of his study of the Camelidae, and he recognized its rela- 

 tionship to earlier Homacodon while suggesting tentatively that the 

 camels may likewise have so originated. Bunomeryx is clearly re- 

 lated to Homacodon but is advanced over the Bridger genus in several 

 respects. The outer cusps of the upper molar teeth, with the styles 

 much more emphasized, appear somewhat crescentic in comparison. 

 The presence of a prominent mesostyle is in marked contrast to the 

 older form. The talon of the upper molars shows a progressive de- 

 velopment of the protoconule, more noticeable in M^ and M^, and a 

 reduction of the hypocone in M^. P"* shows a somewhat more crescen- 

 tic outer wall and the deuterocone in P^ is more pronounced. 



The outer cusps of the lower molars are perhaps a little more 

 crescentic than in Homacodon, and the hypoconid joins the trigonid 

 more conspicuously. The premolars are lower crowned, but the most 

 striking difference lies in the well-developed metaconid of P4 in 

 Bunomeryx, possibly indicating a closer relationship to Microsus. 



BUNOMERYX MONTANUS ^ Wortman, 1895 



Type. — Rostral portion of a skull with P^-IVP on left side and right 

 canine, and left ramus of mandible with P4-M3, A.M. No. 2071. 



5 Illustrated in Peterson, 1919, pi. 36, figs. 3-4. 



