270 KNUT DAHL. 



1) The shape, relations and relative size of the head. 



2) The lenght and slenderness of the tail. 



3) The relation of the anal fin to the length of the tail. 



4) The shape of the caudal fin. 



5) The size of the scales. 



6) The colour. 



Most of these characters will be quite plainly observed on 

 inspection of Pis. II and III. 



As will be easily seen the head of the salmon is smaller, 

 more shapely and narrower than that of the trout. 



The eye of the salmon is situated closer to the forepart of 

 the head than that of the trout; the nasal region is shorter 

 and the mouth smaller than in the case of the tront. 



The upper jaw is also at this stage (as in the previous 

 stage) considerably shorter in the salmon than in the trout. 

 Thus the posterior margin of the upper jaw only seldom reaches 

 as far back as to a perpendicular hne drawn downwards from the 

 posterior margin of the pupil of the eye. The upper jaw of the 

 trout on the contrary, reaches mostly as far back as to the 

 posterior edge of the eye itself and even further back; only in 

 a few cases will its posterior edge touch the limit peculiar to 

 the upper jaw of the salmon. 



The upper jaw of the salmon is also as a rule, a little 

 more drooping than that of the trout. The head of the salmon 

 is also of a more conical, rounded form than the more laterally 

 compressed head of the trout. Thus the cheeks of the salmon 

 as also often the gillcovers are more bulging than in the 

 trout. 



When the salmon has stayed some time in the sea and has 

 grown somewhat, one will find that the frontal part of the head 

 still retains the arch also observed in the smolts, and that 

 this arch will even become more pronounced. Thus salmon 

 of a length of between 20 and 30 cms. actually possess a depression 

 in the occipital region of the head, while the arch of the forehead 



