206 SPECIES IN OUR SALMONIDAE 



of our various forms or races of the Salmonidae, 

 it is proposed to accept Webster's definition of 

 ' species 'as 'an ideal group of individuals re- 

 sembling each other in essential characteristics 

 and capable of indefinitely continued fertile 

 reproduction through the sexes.' 



As examples of extreme divergence of opinion 

 on this subject we may note that whereas Giin- 

 ther, 1866, gives no less than twelve separate 

 species of the genus Salmo, Agassiz, 1834, 

 already restricts the number to three ; while 

 Dr. Day, held by many to be still our best 

 authority, 1 is content with only two, that is, if 

 the chars are left out of consideration. It is 

 proposed, for present purposes, to treat only 

 of the more important of the British salmones, 

 i.e. the salmon, sea trout and common or brook 

 trout, omitting such as the grayling, char, ven- 

 dace, and others of the family. Those admitted 

 by Agassiz were Salmo salar, S. trutta and S. 

 fario \ by Day, the salmon and the sea trout, 

 * and its several varieties, as the brook trout, 

 Loch Leven trout, etc.' 



We have seen above that in the common or 

 brook trout and loch trout we find an infinite 

 variety of colour and marking. The same is 

 found to be the case, if in lesser degree, in the 



1 British and Irish Fishes, 1880-84. 



