SPECIES OF SALMONID.E. 13 



but in this direction the rules have not been strictly adhered to and lack of uniformity 

 and consistency with attendant difficulties still obtain. 



Writing of the genus Salmo, which comprised the Salmones and Salvelini, GUnther 

 (1880, p. 631) said: 'We know of no other group of fishes which offers so many difficulties 

 to the ichthyologist with regard to the distinction of the species as well as to certain 

 points in their life-history, as this genus.' After enumerating the many characters 

 which vary greatly, some of which he considered more or less constant, and referring to 

 a number of problems relating to their life histories, Gunther went on to say (p. 642- 

 643) that 'In accordance with acknowledged principles in zoology, forms which differ 

 from their congeners by a combination of two or more constant characters, are to be 

 distinguished under distinct specific names. Most likely they have been derived, at a 

 not very remote period, from common ancestors, but the question of their specific 

 distinctness is no more affected by this consideration than the question whether Salmo 

 and Coregonus are distinct genera.' Then, in the way of explanation, he added: 'When- 

 ever the zoologist observes two forms distinguished by peculiarities of organization, such 

 as cannot be conceived to be the effects of an external or internal cause, disappearing 

 with the disappearance of that cause, and which forms have been propagated and are 

 being propagated uniformly through all the generations within the hmits of our ob- 

 servations, and are yet most probably to be propagated during the existence of man- 

 kind, he is obliged to describe these forms as distinct, and they will commonly be called 

 species.' 



To me it seems necessary to present the foregoing as exempUfying the commonly 

 accepted ideas regarding the basis of specific distinction, although to a certain extent 

 modified by some later systematists. It is of common experience to find that some 

 species are harder to distinguish than others, and it is not always easy to determine 

 whether certain characters are produced by causes which, being removed, were removed 

 coincidently with the characters. A species of one locaUty easily distinguished from 

 another in the same or another locality, in some other place may appear indistinguishable. 

 Referring to the steelhead {Salmo gairdnerii) and the cut-throat trout {Salmo clarkii), 

 Jordan and Evermann (1896, p. 488) write: 'Among the various more or less tangible 

 varieties and forms of American trout, three distinct series appear which we here pro- 

 visionally retain as distinct species; these may be termed the Cut-throat Trout series, 

 the Steelhead series, and the Rainbow Trout series . . . ' 



'Along the western slope of the Sierra Nevada there are also forms of trout with the 

 general appearance of gairdneri, but with scales intermediate in number (McCloud 

 River), or with scales as small as in the typical mykiss^ (Kern River). In these smaller- 

 scaled forms more or less red appears below the lower jaw, and they are doubtless in 

 fact what they appear to be, really intermediate between mykiss and gairdneri.' 



In the Ught of more recent knowledge, the three series of Pacific trouts may be re- 

 tained, but with different terminology, and distinguished by a different, scale series. 

 The cut-throat or red-throat trout {Salmo clarkii [?j or mykiss Jordan and Evermann) 



'In more recent classification the specific term clarkii replaces mykiss. 



