1915.] Matthew and Granger, Lower Eocene Wasatch and Wind River Faunas. 435 
disappearance of less progressive individuals, and appearance and increase 
of more progressive individuals, seems to be fairly well shown in this 
phylum and in the Cynodontomys-Microsyops phylum, less clearly in some 
others. It is not the gradual replacement of one species by another dis- 
tinct and more progressive species, but so far as one may judge from the 
characters of the teeth the gradual conversion of one species into its suc- 
cessor by the progressive elimination of the more primitive and increase 
in numbers of the more advanced ‘individuals. The detailed geologic 
record of these phyla appears therefore to afford direct proof of continuity 
in their evolution. In the Hyopsodontide, as I have pointed out, it is 
not so precisely continuous, but appears to be rather the gradual replace- 
ment of one species by a more advanced one. 
Pelycodus Cope, 1875. 
Type, Prototomus jarrovt Corr 1874, from the Wasatch of New Mexico. 
The genus is distinguished from Notharctus by the substantially tritu- 
bercular upper molars. The lower teeth are practically indistinguishable 
in approximating species of the two genera. ‘The species increase progres- 
sively in size through the Lower Eocene, but small species likewise appear 
in the later levels, distinguished from those of the earlier horizons by their 
more progressive character. ‘The first appearance of the phylum in the 
known Tertiary succession is in the Sand Coulée beds (P. ralstoni) at the 
base of the Wasatch. The skeleton construction of this species is unknown, 
but in the next stage (P. trigonodus of the Lower Gray Bull) we have asso- 
ciated! skeleton bones which show that the peculiar and characteristic 
structure and proportions of the limb and_foot-bones, especially of astrag- 
alus and calcaneum, was as fully developed as in the latter Notharctide. 
There are several Paleocene genera which might be regarded as ancestral 
or related to Pelycodus on evidence of their teeth alone. But as yet no trace 
of the characteristic skeleton bones of Primates has ever been found in the 
Paleocene, and some of the Paleocene genera which are closest to them in 
dental characters (e. g. Chriacus) are known to be entirely different in 
skeleton, and to pertain not to the Primates but to Creodonta, Condylarthra 
and Insectivora. 
As the evidence stands therefore we must regard the Notharctidé as an 
immigrant family at the base of the Wasatch. 
1 j. e., known to belong to the same individual as the jaws with which they are found. 
