70 SCIENCE SKETCHES. 
say that it is only these Western regions which 
have any trout at all. Of the number of species 
(about twenty in all) which have been indicated 
_ by authors, certainly not more than four can 
possibly be regarded as distinct species; and of 
these four, two are, as will be seen, still extremely 
doubtful. The other names are either useless 
synonymes, or else they have been applied to 
local varieties which pass by degrees into the 
ordinary types. 
Of the American species the Rainbow Trout 
(Salmo trideus) most nearly approaches the Eu- 
ropean Salmo fario. It has the scales compara- 
tively large, although rather smaller than in Sa/mo 
fario, the usual number in a longitudinal series 
being about 135. The mouth is smaller than in 
other American trout; the maxillary, except in 
old males, rarely extending beyond the eye. The 
caudal fin is well forked, becoming in very old 
fishes more nearly truncate. The color, as in all 
the other species, is bluish, the sides silvery in the 
males, with a red lateral band, and reddish and 
dusky blotches. The head, back, and upper fins 
are sprinkled with round black spots, which are 
very variable in number. In specimens taken in 
the sea, this species, like most other trout in sim- 
ilar conditions, is bright silvery, and sometimes 
immaculate. This species is especially charac- 
teristic of the waters of California. It abounds in 
every clear brook, from the Mexican line north- 
ward to Mount Shasta, and occasionally in coast- 
wise streams to Alaska. No specimens have been 
anywhere obtained to the eastward of the Cascade 
