1915.] Matthew and Granger, Lower Eocene Wasatch and Wind River Faunas. ve 
towards the base of the Wasatch, so that it becomes much more difficult to 
distinguish the species and assign them to their proper genera. The Lower 
Eocene species of the family are far less divergent than those of the Bridger, 
and often combine in varying proportions distinctive characters which in 
the Bridger stage have become sorted out into well differentiated and 
distinct genera. In 1909 I based a new genus, Vassacyon, upon one of these 
Wasatch species which combined, characters of Miacis, Vulpavus and Uin- 
tacyon and referred the remaining described species to those genera to whose 
type species they appeared to be most nearly related. I knew at that time 
of a number of undescribed species from the Lower Eocene, but postponed 
description until more and better material should be at hand as a result of 
Mr. Granger’s expeditions. This new material confirms the arrangement 
made in 1909, but shows that in addition to the four genera there noted, 
two others are represented. In every case the species, and especially the 
species or mutants from the older horizons, are more or less synthetic in 
type. 
Had we to deal with the species of Didymictis and Viverravus from the 
Gray Bull, it would be natural to put them under a single genus. But the 
Lost: Cabin species fall into two well distinguished genera. Similarly, if we 
had to deal only with the Gray Bull species of Miacine, they might well 
be included under a single, rather broadly inclusive genus, while the Middle 
Eocene species fall into four clearly distinct generic groups. It might 
seem that the affinities of the Lower Eocene species would be better ex- 
pressed by so uniting them into a single primitive genus from which the 
specialized genera of the Middle Eocene could be derived. But I have 
failed to find any primitive characters which would serve to define such a 
genus in distinction from the Middle Eocene genera already described, and 
have therefore been compelled to distribute the Lower Eocene species for 
the most part, among the specialized genera. That is to say, the evolution 
of the several Miacid phyla was divergent, and not to any extent parallel 
progressive. 
The affinities of the phyla as illustrated by the known species with their 
geological range appear to be about as follows: Mzacis represents the central 
type, from which have diverged a number of specialized phyla, some be- 
coming more predaceous, others frugivorous or omnivorous, as indicated by 
the teeth and other adaptive features of skull and skeleton. Of these, 
Didymictis is the earliest, and presents a succession of species of progres- 
sively larger size and with the carnassial dentition more differentiated, but 
retaining the tubercular dentition much as in Viverra. Viverravus is an 
allied phylum paralleling some of the smaller modern Viverride, with the 
tubercular dentition more reduced; its earlier species show a much more 
