488 Bulletin 4/, United States National Aluseum, 



from 160 to li>0. Back and sides with dark spots. Candal fiu 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 ie 

 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, Sahno galrdncri, 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 irideiis 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, iu 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 baud. 



The Steelhead or f/r((?Y?Hm 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 iu neighboring waters, they are entirely distinct from the 

 "Cut-throat" or myki-'is 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 iodistinguishable, 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 irideiis forms are chiefly contiued to the streams of Cali- 

 fornia and Oregon. The rnylciss series inhabit the waters from Ilnni- 

 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 iu the Great Basin. 



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

 trout with the general appearance of (lairdneri, but with scales interme- 

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

 cal m^/A-iss (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 f/airdneri. 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, 1891): 



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

 recognize any of the distinctions, specitic or Hiihspecific, which have been set up. The present 

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

 vinced that the greater number of the subspecies of Sabuo tnykiss have no sufficient foundation. 



