116 Barriers to Dispersion of River Fishes 
outlets on the summit of a sharp watershed, may serve to 
show us how other lakes, permanent or temporary, may else- 
where have acted as agencies for the transfer of fishes. We 
can also see how it might be that certain mountain fishes should 
be so transferred while the fishes of the upland waters may 
be left behind. In some such way as this we may imagine that 
various species of fishes have attained their present wide range 
in the Rocky Mountain region; and in similar manner perhaps 
the Eastern brook trout* and some other mountain species f 
may have been carried across the Alleghanies. 
The Cassiquiare.—Professor John C. Branner calls my atten- 
tion to a marshy upland which separates the valley of the La 
Plata from that of the Amazon, and which permits the free 
movement of fishes from the Paraguay River to the Tapajos. 
It is well known that through the Cassiquiare River the Rio 
Negro, another branch of the Amazon, is joined to the Orinoco 
River. It is thus evident that almost all the waters of eastern 
South America form a single basin, so far as the fishes are con- 
cerned. 
As to the method of transfer of the trout from the Columbia 
to the Missouri, we are not now left in doubt. 
Two-Ocean Pass.—To this day, as the present writer and 
later Evermann and Jenkins} have shown, the Yellowstone and 
Snake Rivers are connected by two streams crossing the main 
divide of the Rocky Mountains from the Yellowstone to the Snake 
across Two-Ocean Pass. 
Prof. Evermann has described the locality as follows: 
““Two-Ocean Pass is a high mountain meadow, about 8,200 
feet above the sea and situated just south of the Yellowstone 
National Park, in longitude 110° 10’ W., latitude 44° 3’ N. 
It is surrounded on all sides by rather high mountains except 
where the narrow valleys of Atlantic and Pacific creeks open 
* Salvelinus fontinalis Mitchill. 
+ Notropis rubricroceus Cope, Rhinichthys atronasus Mitchill, ete. 
t} Evermann, A Reconnoissance of the Streams and Lakes of Western 
Montana and Northwestern Wyoming, in Bull. U.S. Fish. Comm., XI, 1891, 
24-28, pls. 1 and 1; Jordan, The Story of a Strange Land, in Pop. Sci. 
Monthly, Feb., 1892, 447-458; Evermann, Two-Ocean Pass, in Proc. Ind. Ac. 
Sci., 1892, 29-34, pl. 1, Evermann, Two-Ocean Pass, in Pop. Sci. Monthly, 
June, 1895, with plate. 
