1915.] Matthew and Granger, Lower Eocene Wasatch and Wind River Faunas. qT 
the Gray Bull horizon that I do not doubt its validity. The second speci- 
men shows the unworn premolars and m,, very similar in characters to those 
of T’hinocyon, but in absence of the posterior molars it is not- certainly 
determinate. ) 
A fourth species, which I have placed under Sinopa (S. mordax) is un- 
doubtedly related to this genus, and when better known may have to be 
transferred to it. It shows several characteristic Oxyzenid features, but m3 
is only a little smaller than mz: and has a well developed metaconid. | 
HYANODONTID. 
Sinopa (Stypolophus) is perhaps the most abundant Creodont genus in 
the Lower Eocene and practically the only representative of the family at 
this time. ‘The more specialized 7'rztemnodon is first represented in the Lost 
Cabin beds by a marginal species, 7. whiti@, retaining several characters of 
Sinopa. The hyeenodonts of the Lower Eocene evidently approach the 
Oxyeenide, the two groups being derivable from a common source. ‘This 
is especially seen in the two-rooted pi, of several of the species, and in the 
heavy jaw and Limnocyon-like premolars of S. mordaz. 
Sinopa Leidy. 
The Lower Eocene species of this genus were revised by Matthew 
in 1901 chiefly on the basis of Wyoming specimens. The new collections 
from New Mexico and Wyoming have supplied a large series of specimens 
for comparison. These serve to modify the earlier conclusions in some 
degree. ee | | 
The species are for the most part not very sharply distinguished from 
each other or from those of the Bridger horizons. 
Three new species are here described, and all but one of the described 
species of the Lower Eocene are validated or confirmed by reference to them 
of additional and more complete specimens, topotypes where possible. I 
must confess some doubt however, as to whether all the forms here described 
are entitled to specific rank on the standards used in this revision; or on the 
other hand whether some may not include two or more species which more 
complete material would show to be distinct. It is also possible that more 
than one genus is included. Prototomus Cope 1874, may have to be revived 
to include S. viverrina and probably S. ? secundaria when these species are 
better known. Professor Scott in his recent book appears disposed to 
