NO. 8 UPPER EOCENE ARTIODACTYLA — GAZIN 37 



and P4 in M. scotti, but these are not on a generic level and some, 

 such as the size of teeth and relative size of premolars with respect 

 to molars, are only intermediate between Pentacemylus progressus 

 and P. leotensis. Nevertheless, the lower premolar spacing is greater 

 and characterizes only the forward part of the series in M. scotti, 

 whereas in P. leotensis the diastemata are short and nearly the same 

 between all lower premolars. 



Subfamily Helohyinae (from HELOHYIDAE Marsh, 1877) 



With regard to the suprageneric arrangement suggested in the chart, 

 Helohyiis, though not regarded by all as an homacodont, seems closely 

 allied to the genus Homacodon, so that separation of this short-lived 

 but rapidly evolving stem with full family recognition, I believe, is 

 unwarranted. As a subfamily its relationships are better demonstrated, 

 and at the same time its direction and its distinctness are given recog- 

 nition. I prefer also to include this subfamily along with Homaco- 

 dontinae, under the Dichobunidae, because of the more clearly demon- 

 strable relationship, as indicated in the chart, rather than with the 

 chronologically more remote and distinctive entelodonts. The name 

 Helohyinae is selected rather than Achaenodontinae (Zittel, 1893) 

 as it is based on the older familial designation Helohyidae (Marsh, 

 1877). Moreover, this name does not carry the implication of includ- 

 ing the entelodonts as originally defined, or of being a subfamily of 

 the Entelodontidae as later assigned, as does Zittel's Achaenodontinae. 



Genus ACHAENODON Cope, 1873 



Synonym. — Protelotherium Osborn, 1895. 



Type. — Achaenodon insolens Cope, 1873. 



Discussion. — Achaenodon was described by Cope on the basis of 

 the species A. insolens, from Washakie beds, which he regarded as an 

 arctocyonid creodont. Osborn in 1883 demonstrated its true position 

 to be in the Artiodactyla and, while believing it near the entelodonts, 

 regarded it as belonging in the "ancestral Suidae." Zittel in 1893 

 placed the entelodonts and achaenodonts together in the subfamily 

 Achaenodontinae under the Suidae. Matthew in 1899 proposed full 

 family recognition, Achaenodontidae, distinct from both Suidae and 

 Entelodontidae (Elotheriidae). He was followed in this interpretation 

 by Peterson (1919). More recently Colbert (1938), in his study of 

 Brachyhyops, considered the Achaenodontinae as a subfamily of the 

 Entelodontidae. 



Critical examination of the known Achaenodon material leads me to 



