Barriers to Dispersion of River Fishes 307 



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 f(5r 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. 



t Notropis rubricroceus Cope, Khinichthys atronasii.-i Mitchill, etc. 



t Evermann, A Reconnoissance of the Streams and Lakes of Western 

 Montana and Northwestern Wyoming, in Bull. U. S. Fish. Comm., XI. iSqi, 

 24-28, pis. I and 11; 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, pi. i; Evermann, Two-Ocean Pass, in Pop. Sci. Monthly. 

 June, 1895, with plate. 



