Introduction 



and Salmo salar ouananiche. Various subspecies of Salveltnus 

 fontinalis and of the cut-throat, steelhead and rainbow trouts 

 have been recognized. These forms have, in most cases, perhaps, 

 been regarded as subspecies chiefly because they differed but 

 slightly from related forms. Whether a given form should be 

 regarded as a "species" or a "subspecies" is very much a ques- 

 tion of material, both from a geographic and a numerical point 

 of view, as Mr. Robert Ridgway has well said. With greater 

 material, and from properly selected localities, many forms, which 

 have been considered specifically distinct, are shown to be con- 

 specific; and forms that have been regarded as subspecies are in 

 many instances found to be good species or to have no existence 

 at all. 



The existence of a subspecies implies greater or less geographic 

 or environmental isolation and the presence of intergrading forms. 

 However great the differences may be between two forms, if com- 

 plete intergradation is known to exist, the one is regarded as a 

 subspecies of the other. On the other hand, even though the dif- 

 ferences are slight, if intergrading is not known to exist, they are 

 to be regarded as distinct species. 



Of the various forms of salmon and trout, which we have 

 formerly regarded as subspecies, but few, if any, are known to 

 intergrade with related forms. Although the ouananiche and the 

 Sebago salmon do not differ greatly from the Atlantic salmon or 

 from each other, intergradations are not known. We therefore 

 prefer to regard them as three distinct species, which they prob- 

 ably are. 



The same is true with respect to the various forms of trout 

 in the West; most of those which have been recognized as sub- 

 species are certainly distinct species, while others are of very 

 doubtful validity. Among those whose status is problematical are 

 the Kamloops, Kern River, Shasta and Noshee trouts. They may 

 be species, subspecies or nothing. Investigation of the geographic 

 distribution of the various trout is very much to be desired. 

 While it is not likely the number of species will be reduced, their 

 exact relations need to be made out. 



XXVlll 



