72 SCIENCE SKETCHES. 



trout, we find no differences, other than that the 

 former is of much larger size, and has a larger 

 mouth, and its caudal fin is truncate instead of 

 forked. But the tail becomes more truncate, and 

 the mouth larger with age in .all species of salmon 

 and trout. If a rainbow trout were to reach the 

 size of the steel-head, it ought to acquire charac- 

 ters similar to those of the latter species. Con- 

 versely, unless the rainbow trout are young of the 

 steel-head, the young of the latter are unknown. 

 It is my belief that the steel-head is simply the 

 large rainbow trout which has lived in the sea, and 

 ascends the river to spawn. If this be true, Salmo 

 irideus must be omitted from our lists, as identical 

 with Salmo gairdneri, the latter name being the 

 earlier one. 



The most widely distributed, and decidedly the 

 most important, of the American black-spotted- 

 trout is the Salmo mykiss (== Salmo purpuratns 

 and clarki of authors), or, as we call it, the Red- 

 throated Trout. This species has much smaller 

 scales than the rainbow trout or steel-head, the 

 usual number in a longitudinal series being 150 

 to 170. Its mouth is proportionately larger, and 

 there is usually a narrow band of small teeth on 

 the hyoid bone at the base of the tongue. 

 These teeth are always wanting in Salmo irideus 

 and gairdneri. The color in Salmo mykiss is, as 

 in other species, excessively variable. In almost 

 all specimens there is a deep-red blotch on the 

 throat, between the branches of the lower jaw and 

 the membrane connecting them. This I have not 

 found in other species; and as it seems to be 



