7O 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 irideus) most nearly approaches the Eu- 

 ropean Salmo fario. It has the scales compara- 

 tively large, although rather smaller than in Salmo 

 fario y 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 



