18 Bulletin American Museum of Natural History. [Vol. XXXIV, 
marked approach to the Miacine in the premolar teeth than do the earlier 
species of Didymictis. Uvintacyon is nearly allied to Miacis but with 
trenchant heels on the molars, and progressively reduced premolars. It is 
intermediate in numerous particulars between Viverravus and Miacis. ‘The 
central genus Miacis diverges in the later Eocene into a number of sub- 
genera, the genus thus repeating the differentiation which the family 
Miacidee underwent at an earlier stage. Vassacyon and Vulpavus are 
specializations from the Miacis type towards a more frugivorous mode of 
life paralleling the Procyonide especially Cercoleptes'; the Lower Eocene 
species are closely allied to those of Miacis but Vulpavus is more divergent 
in the Middle Eocene, paralleling Procyon and differentiating into sub- 
genera; Palwarctonyx is a more extreme frugivorous adaptation, paralleling 
Cercoleptes, and probably derived from some species of Vulpavus. Oddectes 
seems to be another specialization from Miacis in somewhat the same 
direction, but with suggestions of insectivorous adaptation. 
The Arctocyonide represent one or more earlier specializations in the 
same direction as these Cercoleptoid and Procyonoid Miacide. But they 
are derivatives not from the Mzacid type, but from an earlier evolutionary 
stage in which the carnassial dentition had not yet specialized. In adapta- 
tion, Clanodon, Thryptacodon and Vulpavus correspond rather closely; so 
do Anacodon and Palearctonyx. But they belong evidently to different 
phyla. 
Key to Genera of Miacide. 
A. Antero-external cusp of p* prominent. Molars $, m2 elongate oval. 
wer ORS. With “Dae heed ek oe. o's hace os a ae ba eee Didymictis. 
BB. “Lower molars with trenchant heels.........:../........-. Viverravus. 
AA. Anteroexternal cusp of p! weak or absent. Molars 3, mz and m; short-oval or 
round. 
B. Carnassials well differentiated, p* extended postero-externally, trigonid of 
of m; high, of ms_3 low. 
C. Lower molars with trenchant heels................... Uintacyon. 
CC. Lower molars with basin heels. 
D. Mz: and m; and heel of m; relatively small, premolars unreduced. 
} Miacis. 
DD. Mbpand heel of m; large, premolars reduced.......... Vassacyon. 
BB. Carnassials little differentiated, pt not extended posteroexternally, 
trigonids of molars similar. 
C. Lower molars with trenchant heels, trigonids high........Oddectes. 
CC. Lower molars with basin heels, trigonids low, my: and ms; and heel 
WES CSUs): eee Rea RR RLU Greets LAC APC a iA iy () Vulpavus. 
CCC. Lower molars flat topped, premolars much reduced. . . . Palearctonyz. 
1JT take occasion to note that the expression ‘‘Cercoleptoid Miacidse’’ does not involve 
any hypothesis that Cercoleptes is descended from this group, but merely that the teeth 
show a similar adaptation. 
