1895.] Leuciscus Balteatus, A Study in Variation. 23 
tions are found at Little Spokane, where the extent of varia- 
tion is much smaller. A priori such symmetry or approach to 
symmetry is to be expected for each locality, but the devia- 
tions from it are many and great. The many shoulders and 
peaks in localities PA which but few specimens have been 
collected, indicate probably nothing so much as the lack of a 
sufficient number of specimens. When but ten specimens are 
examined, each specimen, more or less, makes such a vast 
difference in the character of the curve that the localities with 
less than 20 specimens may be dismissed without further 
notice. 
Aside from curves, such as that of Little Spokane, where a 
certain number of rays is the predominant one, we have curves 
such as that of the Payette River, where the number of speci- 
mens having 16, 17, 18, 19 and 20 rays, is nearly equal. Still 
another type of curve is represented by the curves for Lake 
Washington, Colville and Umatilla, in which two numbers 
predominate, with the intervening numbers in minority. The 
conditions are most marked at Umatilla, where we have two 
incipient varieties with 18 and 21 as the predominating num- 
ber of rays. 
I have given, at the outset, the probable causes which have - 
brought about the great differences between the Pacific slope 
fishes. 
We must look to other causes for the great variation betweem 
species of undoubted Atlantic origin, and especially the varia- 
tion in the same species, which reaches its culmination in 
Leuciscus balteatus and Agosia nubila. The climatic, altitudinal — 
and geological differences in the different streams, and even in 
the length of the same stream, are very great on the Pacific 
slope. To these different environments we must attribute the 
conditions set forth in the present paper for Leuciscus balteatus. 
These differences in different localities in the same stream can 
only become established in nonmigratory species. No such 
differences are to be expected for a migratory species. To a 
migratory species, such as the species of Salmo, different 
rivers bear the same relation as different localities on the 
same river to a non-migratory. Isolation for the specimens of 
