456 Mesozoic and Cenozoic of North America. [ May 
imperfect observation, or slight difference of age. Thus, in the 
Central Dakota area, Hyznodon, Hyracodon, and Poébrothe- 
rium have not yet been found. In the Canadian tract57 neither 
of these forms has been found, and a genus of Creodonta (Hemip- 
salodon) is as yet peculiar to it. The thickness of the beds is 
as follows: ; 
Feet. 
Nebraska (Hayden) 5 i ; 150 
Central Dakota (Cope) 200 
The White River series corresponds to the Oligocene of some 
authors. Thus there occur in both Europe and America at this 
period the genera Elotherium, Hyænodon, Cynodictis, Ischy- 
romys (= Sciuromys teste Schlosser in litt.), ? Pterodon (? Hemip- 
salodon teste Schlosser in litt.), and Agriochcerus (? Haplomeryzx). 
Other European Oligocene genera occur in the John Day series, 
as Meniscomys (= Sciurodon teste Schlosser in litt.) and (? = Ael- 
urogale) Archzlurus (Schlosser in litt.). 
Jous Day.—Mammatlia. Presence of Nimravidz, Poébrothe- 
riide, Tragulide, Elotheriide, Suide, Muridæ, and Saccomyide. 
Absence of Lemuroidea and Creodonta; of Hystricide, Felidz, 
Ursidz, Camelidz, Equidz, and Proboscidia.53 
This formation occupies a considerable tract on the upper part 
of the course of the John Day River in Oregon. King states 
that it extends north into Washington and south into Nevada, 
but, according to White, the beds from the latter State, to which 
King gave the name Truckee, are of later age. According to 
Marsh the John Day beds have a thickness of four or five — 
thousand feet. The vertebrate fauna is very rich. 
The beds in the valley of the North Fork of the John Day 
River present some faunal peculiarities, but their significance is 
unknown.? 
TicHo.ertus.°—Mammalia. Presence of Anchitherium, Pro- 
boscidia, and Camelidz, and the Oreodont genera Merycochcerus, 
Merychyus, Cyclopidius, and Pithecistes. Absence of ? Elothe- 
` riidæ, ? Poébrotheriidz, ? Nimravidz, and Cosoryx. 
This horizon requires further exploration, as but twenty species — 
have been thus far determined from it. But it is evidently inter- 
mediate in age between the John Day and Loup Fork epochs, 
with greatest affinities to the latter.© It differs from the latter 
in the presence of Anchitherium and numerous genera and 
