458 Mesozoic and Cenozoic of North America. [ May 
Two others are probably contemporary with one or both of 
the preceding, so that the names have only a provisional utility. 
Megalonyx beds. 
Truckee. 
IpaHo.°—Present : Mammals, Camelidz, Eguus excelsus; Fishes, 
Cobitidz, Percide, Siluridæ, Raiide, Mylocyprinus (Cyprinide), 
and peculiar species of existing genera of Cottidz, of Salmon- 
ide, Catostomidz, and Cyprinidae Absent: mammals, E/ephas 
primigenius, etc. 
ammalian fauna of this epoch is little known, owing to 
the rarity of remains. Its characters may be chiefly learned 
from the numerous fresh-water fishes it contains, by which it may 
be compared with the Equus beds, which also contain many 
fish remains. But one area of this epoch is known. It covers 
the southern part of Western Idaho, entering Eastern Oregon. 
TruckEE.—The typical locality of this formation is the Kaw- 
soh Mountains in Western Nevada. The formation was supposed 
‘by King to be identical with the John Day Miocene, but Dr. C. A. 
White informs me that it is of much later age. Vertebrate remains 
have been found, but have not been fully determined. Thickness 
(King), two thousand three hundred feet.” 
Equus Beps.”"—Present: Glyptodontide (Mexico), Megathe- 
riidez, Eschatiide; extinct genera, Holomeniscus, Mastodon 
(Mexico), Smilodon (Texas); extinct species, Elephas primi- 
genius ; Equus, four species; Lutra, Cervus, etc.; recent species 
of Thomomys, Arvicola, Castor, Canis,? Homo. Absent: Coso- 
ryx, Oreodontidz, Protolabididz ; Raiidz, Cobitidæ, Mylocypri- 
nus, and the fishes of the Idaho beds in general ; Castoroides and 
Amblyrhiza.” 
The- localities of this formation are widely distributed. In 
the presence of various extinct forms, above mentioned, it 
agrees with the Pampean fauna of South America, but differs 
in the presence of the northern existing genera and species 
with the extinct Elephas primigenius. The Argentine forms drop 
off successively as we travel northwards. Thus, Macrauchenia 
ceases in Bolivia, Toxodon in Nicaragua (Leidy), Glyptodon in 
the valley of Mexico (Barcena), where Elephas primigenius com- 
mences. Where the line should be drawn between the Pampean 
and Equus beds I do not know, but we can arbitrarily assume it 
to be the line of distribution of the Elephas primigenius. This will 
