EXPLOEATIONS IN COLORADO AND UTAH. 
13 
they came from some point on the South Platte, and on this supposition I have adopted 
the name stoniias for the trout of the Platte. 
The green back trout seldom exceeds three-fourths of a pound in weight. It is very 
abundant in the streams of the Upper Arkansas as well as in the Twin Lakes. It 
spawns in spring, in snow-water if possible, and it will leave spring- water to find snow- 
water. In winter, however, they seek for warmer waters. It is said that when the 
winter breaks up, the trout are too blind to see bait. In color, the green-back is 
green, or even almost black on the back. The lower fins and the throat are bright red, 
but tliere is not much trace of the red lateral band. The black spots are large and 
mostly confied to the posterior part of the body. In some cases these spots are ocellated 
with paler. At the spawning time, in May and early June, the males have much red, 
but later the sexes become similar. In specimens found about pools, there is often 
much red even in the summer. Those from the deeper parts of the lakes are always 
bright green, with a little red. 
At the hatchery of Dr. Laws it appears that this trout will not willingly eat young 
suckers or minnows, its food being largely young Crustacea. 
The flesh in these trout is extremely red, this color being probably heightened by 
tlie character of its food. In the specimens from Arkansas Eiver the body is plum[»er 
and softer than in those from Twin Lakes. 
In connection with our study of these two forms I have iiad occasion to compare a 
large number of trout from various streams in the Eocky Mountains and westward. 
Besides the rainbow trout, Salmo irideus, which is chiefiy confined to California, and 
the steel-head trout, Salmo gairdneri, found chiefiy about the river-mouths in Oregon 
and northward, both of which species are characterized by the large size of the scales 
(from 130 to about 140), all our other western trout of the genus Salmo seem to belong 
to a single species. For this species the oldest scientific name is that of Salmo mylHss 
Walbaum (1792). To this name Salmo purgniratus (Pallas, 1811) and Salmo claricii 
(Richardson, 1830) must give precedence. 
This species is distributed from Kamtschatka and Alaska, southward to the mount- 
ains of Chihuahua, and eastward along the flanks of the Eocky Mountains so far as the 
clear water of the mountain goes. It seems to be absent in southern California, its i)lace 
being taken by the irideus, but in all other suitable waters, excepting some streams in 
north western Wyoming, where water-falls keep it back, this trout may be found. 
Several well-marked varieties occur in isolated lakes, and in general large streams 
or streams with a large food supply yield larger trout than small streams or streams 
with scanty food. All forms of Salmo myhiss hav^e distinct hyoid teeth in life. All 
have a red dash below the lower jaw, from which comes the vernacular name of “cut- 
throat trout,” and all show a small diffuse dark spot behind the eye. 
A comparison of many specimens leads us to the recognition of the eight sub- 
species or varieties besides two others which I am scarcely able to define. It will be 
interesting to find out to what extent these forms will interbreed, and to what degree 
their x^eculiar characters will prove to be permanent when they are transplanted to 
other waters. 
a. Salmo mykiss (Walbanni.) (Pl.ate I, Fig. 3.) 
The typical U. e., first known) form of the species, found in the waters, both fresh 
and salt, of Alaska and Kamtschatka. 
