SPECIES AND GENERA. 37 



so on, that can easily be observed. It must not therefore 

 be supposed that the points I here notice are in all cases 

 the ones with regard to which the classification of the 

 fish has been decided. , 



It is necessary to know the names of the fins, and 

 the signification of the other terms used in these de- 

 scriptions. 



By referring to Plate 10 it will be seen that the fin 

 on the back of the fish is termed the " Dorsal fin." 

 There may be one or two dorsal fins ; of which the 

 hindmost may bo an adipose, or gristly fin, without 

 rays. 



The fin opposite to the dorsal, on the lower surface 

 of the body, is termed the Anal fin. 



The fin at the end of the tail is the Caudal fin. 

 (NJB. The tail of a fish is understood to be that part of 

 the body between the anal and the caudal fins, it is a 

 mistake to call the fin itself the tail). 



These comprise the vertical fins, the remaining fins 

 are disposed in pairs, and answer to the four limbs of 

 a quadruped. The upper pair are termed the Pectoral 

 fins, the lower pair are called the Yentral fins. 



In taking measurement the following rule has been 

 observed: — By the u total length" I understand the 

 length in a straight line from the end of the snout to 

 the base of the caudal fin ; that is to say, the total 

 length not including the caudal fin. This affords a 

 better standard of comparison, as the fin is frequently 

 damaged, or may vary slightly in length, than if the 

 fin were included. 



