1903.] STANTON—MOLLUSCAN FAUNULE. 189 
basin, as is indicated by their apparent distinctness from all de- 
scribed species. 
According to the labels the fossils all come from one locality on 
Wettacombe’s ranche near Harlowton, on the Musselshell River, 
Montana, where they were collected by Dr. M. S. Farr and Mr. 
A. Silberling. The interesting Mesozoic and Tertiary section of 
this region lying in Sweetgrass county, east of the Crazy Moun- 
tains and south of the Big Snowy Mountains, has been somewhat 
fully described by Mr. Earl Douglass,' who states that the Fort 
Union, the Laramie and the familiar Meek and Hayden section of 
the marine Upper Cretaceous are well represented. Beneath the 
Fort Benton formation is a thick series—‘‘ many hundreds of feet ”’ 
—of sandstones and shales, of which the upper part is supposed to 
represent the Dakota and the lower part—‘‘ largely red in color ’’ 
—yielded bones of large Dinosaurs, fossil wood and these inverte- 
brates. Douglass refers this part of the section with doubt to the 
Jurassic, though he states that the vertebrate remains have not been 
studied. I have not been informed as to whether the mollusks and 
vertebrates occur in exactly the same bed. Apparently the ex- 
posure does not extend to beds as low as the marine Jurassic, which 
is known to occur in this general region, and which belongs to the 
upper part of the Jurassic system. 
It is evident from the above statement that the fresh-water 
horizon in question lies somewhere between the marine Upper 
Jurassic and the Fort Benton, which may be correlated with the 
Turonian of Europe. This interval, covering the lower part of the 
Upper Cretaceous, all of the Lower Cretaceous and possibly the 
latest Jurassic, is not represented by marine strata in the northern 
interior region. Instead there is a number of non-marine forma- 
tions in various parts of the region, whose relationships to each 
other are obscure, their principal point of resemblance in most 
cases being an apparently similar stratigraphic position. 
Since in other parts of the continent this interval includes the 
equivalent of the Comanche series, consisting of several thousand 
feet of marine sediments and containing a number of distinct 
faunas, it is evident that there is room for many distinct horizons 
of fresh-water beds, and it would not be surprising if those of dif- 
ferent ages were in some cases developed in different parts of the 
1 Sctence, n. s., Vol. XV, pp. 31 and 272, January 3 and February 14, 1902; 
Proc. Amer. Philos. Soc., Vol. XI, pp. 207-224, 1902. 
