Salmonidag 97 



The rainbow forms are chiefly confined to the streams of 

 California and Oregon. In these the scales are large (about 135 

 in a lengthwise series) and the head is relatively large, forming 

 nearly one -fourth of the length to base of caudal. These enter 

 the sea only when in the small coastwise streams. Usually 

 they have no red under the throat. The cutthroat forms are 

 found from Humboldt Bay northward as far as Sitka, in 

 the coastwise streams of northern California, Oregon, Wash- 

 ington, and Alaska, and all the clear streams on both sides 

 of the Rocky Mountains, and in the Great Basin and the 

 headwaters of the Colorado. The cutthroat-trout have the 

 scales small, about 180, and there is always a bright dash of 

 orange-red on each side concealed beneath the branches of the 

 lower jaw. Along the western slope of the Sierra Nevada there 

 are also forms of trout with the general appearance of rainbow- 

 trout and evidently belonging to that species, but with scales 

 intermediate in number (in McCloud River), var. shasta, or with 

 scales as small as in the typical cutthroat (Kern River), var. 

 gilberti. In these small-scaled forms more or less red appears 

 below the lower jaw, and they are doubtless what they appear to 

 be, really intermediate between clarkii and irideus, although 

 certainly nearest the latter. A similar series of forms occurs in 

 the Columbia basin, the upper Snake being inhabited by clarkii 

 and the lower Snake by clarkii and rivularis, together with a 

 medley of forms apparently intermediate. 



It seems probable that the American trout originated in 

 Asia, extended its range to southeast Alaska, thence southward 

 to the Fraser and Columbia, thence to the Yellowstone and 

 the Missouri via Two-Ocean Pass ; from the Snake River to the 

 Great Basins of Utah and Nevada; from the Missouri south- 

 ward to the Platte and the Arkansas, thence from the Platte 

 to the Rio Grande and the Colorado, and then from Oregon 

 southward coastwise and along the Sierras to northern Mexico, 

 thence northward and coastwise, the sea-running forms passing 

 from stream to stream. 



Of the American species the rainbow trout of California 

 (Salmo irideus) most nearly approaches the European Salmo 

 fario. It has the scales comparatively large, although rather 

 smaller than in Salmo fario, the usual number in a longitudinal 



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