NATURAL HISTORY OF BRITISH SALMONID^E. 157 



and more numerous than in the other two species, the bull trout 

 possessing the longest and strongest of the three fish, and the 

 salmon those of medium size short, stout, and pointed. 



Thirdly, as to fins. The shape and size of the tail fins are 

 a less certain test in some respects than the teeth, as they vary 



A, the pectoral or breast fins (so called from their being placed on the breast or 

 shoulder of the fish) ; E E, the dorsal or back fins ; n, the ventral fins (named 

 from their position on the belly); c, the anal fin (placed close behind the anal 

 aperture) ; D, the caitdal or tail fin ; F marks the lateral or side line. 



much in different stages of growth. They will, however, be 

 found a great aid to other distinguishing characteristics. They 

 are usually as follows : 



SALMON'. 



Tail fin : deeply forked 

 when young, less so 

 at third year : at fifth 

 year nearly or quite 

 square. 



BULL TROUT. 



Becomes square at an 

 earlier period than in 

 salmon, and after- 

 wards gradually con- 

 vex. 



SEA TROUT. 



Less forked than in 

 salmon of same age ; 

 becomes ultimately 

 square. Tail shorter 

 and smaller than in 

 salmon. 



The shape and position of the other fins likewise differ, as 

 will be seen by a comparison of the descriptions which follow: 



SALMON. 



Dorsal fin : Hinder ori- 

 gin about half-way be- 

 tween point of nose 

 and end of tail fin. 

 Third ray longest. 



Adipose fin : Hinder 

 origin half -way be- 

 tween origin of last 

 back-fin ray and end 

 of tail fin. 



BULL TROUT. 



Commences about half- 

 way between po ; nt of 

 nose and origin of 

 unper tail fin rays. 

 Base of dorsal longer 

 than longest ray. 



Xearer to end of tail fin 

 than to origin of last 

 dorsal-fin rav. 



SEA TROUT. 



Hinder origin exactly 

 half-way between point 

 of nose and end of 

 tail fin. Second ray 

 longest ; same length 

 as base of fin. 



Half-way between origin 

 of last ray of back fin 

 and end of tail fin. 



