4 Bulletin American Museum of Natural History. [Vol. XXXIV, 
to the Wasatch faune and most if not all of its genera are represented by 
more perfect material of related, possibly identical, species in this country. 
The lower Eocene mammals of the rest of the world are totally unknown.! 
This series of contributions deals therefore with practically all that is 
known to science of the Lower Eocene mammalia. The authors, while in 
entire accord as to their conclusions, are separately responsible for the 
sections of the revision appearing under their individual names, and it is 
requested that they be so quoted. 
PART I— ORDER FER (CARNIVORA). SUBORDER CREO- 
DONTA. 
By W. D. MatTruew. 
The Creodonta of the Eocene form a relatively compact order, whose 
affinities are well understood, owing chiefly to the more or less complete 
knowledge of the skeleton of the principal genera. The affinities and 
classification of the several families were discussed at some length by the 
writer, in the memoir on the Bridger Carnivora and Insectivora2 The new 
material from the Lower Eocene confirms in detail the views there set forth, 
and illustrates very clearly the progressive stages in the differentiation of the 
several groups during the successive horizons of the Lower Eocene. The 
more complete material now at hand clears up the affinities of several 
doubtful groups, notably of the Oxycleenidze, some of which at least appear 
to be nearly related to the Arctocyonidz. These two families should proba- 
bly be united, but a further study of the Paleocene Creodonta with the new 
and more complete material now at hand is desirable before this change is 
made. 
Only one Paleocene Creodont has been known hitherto to survive into 
the Wasatch formations. To this genus, Didymictis, we are now able to 
add two others, Dissacus and Chriacus, while the new genns Thryptacodon 
is distinctly a Paleocene type. No trace of any Pseudocreodine genus is 
found in the Paleocene except in the transitional Clark For: beds, but the 
Kucreodi and Acreodi of the older Torrejon and Puerco faunas are more 
nearly related to those of the later horizons than had previously appeared. 
1 The Notostylops fauna of Patagonia I regard as late Eocene if it is a faunal unit at all. 
2 Carnivora and Insectivora of the Bridger Basin, Middle Eocene. By W. D. Matthew. 
Mem. Am. Mus. Nat. Hist., Vol. LX, part vi, August, 1909. 
