The Trout of Western America 



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

 the headwaters of the Colorado. Along the western slope of the 

 Sierra Nevada there are also forms of trout with the general ap- 

 pearance of steelheads, but with scales intermediate in number (in 

 McCloud River), or with scales as small as in the typical cut- 

 throat (Kern River). 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 gairdneri, 

 A similar series of forms occurs in the Columbia basin, the upper 

 Snake being inhabited by clarkii and the lower Snake by clarkii 

 and gairdneri, together with a medley of intermediate forms. 



It seems not improbable that the American trout originated in 

 Asia, extended its range southward to the upper Columbia, thence 

 to the Yellowstone and the Missouri via Two-Ocean Pass; from 

 the Missouri southward to the Platte and the Arkansas, thence 

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

 from the Colorado across the Sierras to Kern River, thence north- 

 ward and coastwise, the sea-running forms passing from stream 

 to stream as far north as the Fraser where the Kamloops trout 

 would mark one extreme of the series, and re-entering as a dis- 

 fcmct species waters long occupied by typical clarkii. 



The various forms of cut-throat trout have usually been re- 

 garded merely as subspecies of the species originally described as 

 Salmo clarkii, but as none of them is really known to intergrade 

 with any other we now think it best to consider them all as 

 distinct species. Most of them certainly are good species while 

 a few others may prove wholly undefmable. 



a. Black spots almost as numerous on the head as on the pos- 



terior part of the body. 



b. Scales usually about 160 to 170. 



c. Spots rather large, irregular and profusely scattered, usually 



none on the belly. 



d. Red marks under ientary bones always present. 



e. Black spots encroaching somewhat on belly; clarkii, 176 



ee. Black spots not encroaching on belly ; lewisi, 179 



dd. Red marks under dentary bones obsolete or nearly so; 



gibbsii, 1 79 

 cc. Spots rather large, sparsely scattered, some on belly and 



lower side of head ; henshawi, 180 



bb. Scales very small, about 200 transverse series; tahoensis, 181 



