808 The American Naturalist. [September, 
found it in the Yellowstone Valley in 1883. The Canadian 
geologists report it from numerous points in what they call 
Laramie in the Northwest Territory, which I believe to be nearly 
or quite the same as the Fort Union group. As Dr. Newberry 
is not willing to admit the Laramie age of this group, and 
inclines to regard it as Tertiary, this may also pass as an 
Eocene species. It is not, however, strictly confined to the 
Eocene, for it has recently been found in a collection from 
the John Day River, Oregon, a Tertiary deposit that is gener- 
ally placed near the top of that system as Pliocene or extreme 
upper Miocene. On the other hand, the variety integrifolia Lx. 
is a Laramie form from Black Buttes and Golden, and is there- 
fore Cretaceous. 
P. haydenii Newberry has very much the same range as the 
last, chiefly Fort Union group and Canadian Laramie, but it has 
not been found higher, and has been reported from certain doubt- 
ful deposits, such as Carbon, Medicine Bow, and Washakie, in 
Wyoming. It also occurs at Golden, and is said to be found in 
the typical Laramie of the Raton Mountains. 
P. gulielme Göpp. is a well-known and widely distributed 
species of the European Miocene, also abundant in all the Arctic 
Tertiaries. Nathorst finds it in the Upper Tertiary of Japan, and 
it is by no means rare in the American deposits, being reported 
from Carbon, Washakie, Separation, Medicine Bow, Junction 
Station, etc., in Wyoming, perhaps Lower Tertiary ; from Golden, 
probably Denver formation; and with less certainty from Black 
Buttes and the Raton Mountains, true Laramie. I collected it 
on the Lower Yellowstone, Fort Union group, and Lesquereux 
identified it in a collection from Mansfield, Louisiana (Mississipp! 
Tertiary). It therefore appears to originate in the Upper Creta- 
ceous. ; 
Finally the Miocene and Pliocene species are. 
P. aceroides (Göpp.) Heer. This is the most abundant u all 
fossil planes, and, accepting Professor Jankó's synonymy, 15 ex- 
tremely variable. It is doubtless the immediate ancestor of all 
the living species, but it is not an exclusively Miocene and Plio- 
cene species, as it occurs abundantly throughout the Arctic 
