264 KNUT DAHL. 



In specific determination however, I would not advise 

 anybody to attach importance to any one of these characters 

 isolated, hut only to a careful examination of them all. 



PI. I represents two fishes in natural size. Ttie upper one 

 is a trout, the lower a salmon, both caught in the river Gula 

 (the mouth). If we compare them the great difference in form 

 of the body is obvious. 



While the trout is more plump and has a shorter and clumsier 

 tail, the salmon is more finely pointed and spoolshaped in form, 

 and has a very slender and relatively long tail. The salmon is 

 not so much laterally compressed as the trout, which however 

 cannot be shown in the drawing. 



The shape of the head is utterly different in the two spe- 

 cies. The head of the young salmon is low and slender, while 

 that of the trout is higher and clumsier. The head of the trout 

 is relatively larger than that of the salmon. At first sight the 

 head of the salmon seems specially long. In comparing the 

 fishes it will however be seen, that the head of the salmon seems 

 long, because its facial region (the nose and the mouth-region) 

 is considerably shorter than that of the trout, the gillcovers being 

 longer. 



The eye of the salmon, proportionally larger than that oE 

 the trout, is pushed very much forward. The nose is specially 

 short and the mouth small. This latter character is expressed 

 in the upper jaw of the salmon being exceedingly short. If a 

 perpendicular line is drawn downwards from the posterior part of 

 the pupil of the eye, the posterior edge of the upper jaw will as 

 a rule, not reach far enough back to touch this line. Often it 

 will only reach as far back as to touch a perpendicular line 

 drawn downwards from the centre of the pupil. In the trout 

 however the frontal part of the head is considerably longer, the 

 nose being proportionally longer and the mouth region heavier. 

 The mouth is larger, and the upper jaw consequently longer. 



