2 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 128 



Striking growth with transition to forms such as Achaenodon, and 

 may also have given rise to the Oligocene entelodonts, possibly through 

 the long-snouted Lophiohyus. Included in the helohyid line is the 

 closely related Parahyus, now generally and probably erroneously at- 

 tributed to the lower Eocene. The selenodont forms appear in the 

 North American upper Eocene represented by at least five families. 

 These include the hypertragulid, Simimeryx ; the agriochoerids, Pro- 

 tor eodon and Diplobunops; two distinctive groups hitherto admitted 

 together in the Camelidae, including on the one hand the poebrotherine 

 camelid, Pochrodon, and on the other the oromerycids, Oromeryx, 

 Protylopiis, Camelodon, and Malaquiferiis; and the leptomerycids, 

 Leptotragulus, Leptoreodon, and Poahromylus. Protoreodon is by all 

 odds the most frequently encountered and most abundantly repre- 

 sented in collections. In lesser numbers, but not uncommon, are 

 Protylopiis, Leptotragulus, and Pentaceniylus. 



Interest in the upper Eocene artiodactyls was stimulated by an ex- 

 ceptionally good representation of these forms obtained by the Smith- 

 sonian Institution in 1938 from the upper or "C" horizon of the Uinta 

 formation. The bulk of the material came from a single quarry in 

 Myton pocket, approximately 7 miles east of the town of Myton in 

 the Uinta Basin of northeastern Utah. During routine identification 

 of these specimens for purposes of cataloging, it became evident that 

 there was marked taxonomic confusion and that the systematic ar- 

 rangement applied to the artiodactyls of this age was in much need of 

 revision. 



It may be noted that this study is based for the most part on dental 

 characters, so that it may be looked upon as essentially an odonto- 

 graphic revision. Other details of skeletal anatomy are, of course, 

 extremely important to a better understanding of relationships, but 

 only a few of the forms involved were represented by anywhere near 

 adequate skeletal material so that the additional information obtained 

 of these could not be fully utilized on a comparative basis. A detailed 

 investigation of the skeletal anatomy of the better-represented forms 

 might well form the basis of a separate study, and was indeed 

 planned by Scott ^ (see 1945, pp. 233 and 236). 



ACKNOWLEDGMENTS 



This review has been aided immeasurably by the courtesies extended 

 by various museums and universities in permitting me to borrow for 



1 A study of the Uinta fauna as a whole was under way by Professor Scott 

 at the time of his death, and considerable manuscript had been prepared. 



