488 



TELEOSTEI 



[CH. 



To give an account of the classification of an enormous group 

 like the Teleostei would far exceed the limits of this book ; the 

 latest authority (Tate Regan) recognises no less than 35 primary 

 divisions, and it would be useless, even if it were possible, for the 

 student to memorise the characters of all these. All we can 

 attempt to do is to give some account of some groups, mainly of 

 those which are of economic importance, because they constitute an 

 important source of food. Before doing so we may briefly mention 



GUI slits 1-5 



"Epibnanchia/ 



^%' 



Afferent 

 Arteries 

 1-4 



Dors&l 

 Aorta. 



FIG. 239. 



Diagram illustrating the arrangement of the heart and branchial 

 vessels in a Teleostean fish. 



some of the characters which are relied on by taxonomists in 

 dividing Teleostei into groups. 



First in importance of these must be reckoned the position of 

 the pelvic fins. In primitive forms these are placed a considerable 

 distance behind the pectoral fins as in Chondrichthyes. This position 

 is known as the abdominal one. But in very many Teleostei the 

 pelvic fins are moved forward until they are immediately behind 

 the pectoral fins and the pelvic girdle articulates with the cleithra. 

 This position is known as the thoracic one. In some families (as 

 for instance in the Cod family, and in the Flat-fish family) they are 



