488 Bulletin 47, United States National Museum. 



from 160 to 190. Back and sides with dark spots. Caudal fin subtrun- 

 cate or with shallow fork. 



A very widely distributed species, found in all clear streams of the 

 Rocky Mountains and Sierra Nevada, from Kamchatka and Alaska to 

 Chihuahua and northern California, and often entering the sea. It is 

 exceedingly variable, being subject to many local changes, and its 

 extreme forms show a degree of variation rarely met within the limits 

 of a single species. 



Among the various more or less tangible varieties and forms of Ameri- 

 can trout, three distinct series appear which we here provisionally 

 retain as distinct species; these may be termed the Cut-throat Trout 

 series, the Steelhead series, and the Rainbow Trout series. The Steel- 

 head series, Salmo gairdneri, is characterized by moderate scales (150 

 to 180 series), moderate mouth, red lateral band and the absence of red 

 between the branches of the lower jaw. The irideus or Rainbow Trout 

 series has usually large scales, small mouth, a red lateral band and 

 usually no red below the lower jaw. The Cut-throat Trout, Salmo 

 mykiss, in its various forms, has smaller scales (150 to 190 series), a larger 

 mouth, always a distinct red blotch between the branches of the lower 

 jaw, and usually no red lateral band. 



The Steelhead or gairdneri series is found in the coastwise streams of 

 California and in the streams of Oregon and Washington, below the 

 Great Shoshone Falls of the Snake River. In the lower course of the 

 Columbia, and in neighboring waters, they are entirely distinct from the 

 "Cut-throat" or mykiss forms, and no one could question the validity of 

 the two species. In the lower Snake and in other waters east of the 

 Cascade range, the two forms or species are indistinguishable, being 

 either undifferentiated or else inextricably mingled. The proper inter- 

 pretations of these facts, lately discovered by Dr. Gilbert, is yet to be 

 shown. The irideus forms are chiefly confined to the streams of Cali- 

 fornia and Oregon. The myJciss series inhabit the waters from Hum- 

 boldt Bay northward, the coastwise streams of northern California, the 

 head waters of the Columbia and Snake rivers, and all the clear streams 

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



Along the western slope of the Sierra Nevada there are also forms of 

 trout with the general appearance of gairdneri, but with scales interme- 

 diate in number (McCloud River), or with scales as small as in the typi- 

 cal mykiss (Kern River). In these smaller-scaled forms more or less red 

 appears below the lower jaw, and they are doubtless in fact what they 

 appear to be, really intermediate between mykiss and gairdneri. A simi- 

 lar series of forms occurs in the Columbia Basin, the Upper Snake being 

 inhabited by mykiss, the lower basin of the Snake, as above stated, by 

 gairdneri and mykiss, together with a medley of intermediate forms. 



Concerning the trout of the Upper Columbia Basin, Gilbert and Ever- 

 mann observe (Investigations Columbia River Basin, 50, 1894): 



"With every additional collection of black -spotted trout it becomes increasingly difficult to 

 recognize any of the distinctions, specific or subspecific, which have been set up. The present 

 collection [from Idaho and Washington] adds not a little to the difficulty. We are now con- 

 vinced that the greater number of the subspecies of Salmo myhiss have no sufficient foundation. 



