22 



BRITISH FRESHWATER FISHES 



each ray is now attached to its own support ; the 

 pelvic radials also are small or absent, and some or 

 all of the rays are directly inserted on the pelvic 

 bones ; finally, the caudal fin is ' homocercal,' i.e. 

 the upturned end of the tail has become so short 

 that the fin is mainly formed of rays which were 

 originally inferior, but are now terminal. 



The more generalized Teleostean fishes may be 



---^ 



Fig. 4.— Pelvic fin (A) and anal fin (B) of a Trout. 

 b. basal bones ; r. radials ; d. dermal rays. 



characterized by the terms, Pkysostomi, Malacopteri, 

 Abdominales. That is to say, the air-bladder com- 

 municates with the alimentary canal by means of a 

 duct, the fin-rays are flexible and jointed, and the 

 pelvic fins, when present, are placed far back. 



Of several orders possessing these features four are 

 represented in the rivers of the British Isles, namely, 

 the Isospondyli, including the Salmon family {Salmon- 

 idce), the Smelt family {Argent midd), and the Herring 



