Classification 207 



be stated that the surest external physical charac- 

 teristic which may be said to be constant in each 

 species and by which identification is assured, is 

 the size of the scales as shown in the number of 

 vertical series between the front of the dorsal 

 fin and the lateral line ; but as these scales are 

 almost microscopic in most of our American 

 trouts, and as the skin on the back of old male 

 trouts is apt to become spongy and thick, the 

 scales becoming invisible from being embedded 

 in the skin, this test is beyond the reach of the 

 ordinary angler on the stream. 



The ichthyologist seeks for correct classifica- 

 tion of Salmonid^e primarily in the number of 

 vertebrae; the number of pyloric appendages, or 

 blind sacs opening into the alimentary canal ; 

 the form of the preopercle or anterior gill cover; 

 width and strength of the maxillary or upper 

 jaw ; size of teeth and their arrangement and 

 permanence on the vomer — the bone on the 

 roof of the mouth ; the development or absence 

 of teeth on the hyoid bone at the base of the 

 tongue ; size and number of scales, as above 

 stated ; development of the pectoral and caudal 

 fins ; the number of gill-rakers, a series of bony 

 appendages along the inner edge of the gill 



