192 THE STORY OF FISH LIFE. 



or fishes with the mouth parts composed of 

 separate bony elements. The Teleostomi have the 

 body clothed with symmetrical plates or scales, 

 and a single gill opening covered with a shield- 

 shaped plate. 



The autostylic group of fishes are similarly 

 divided into two sub-classes — the holocephali, or 

 whole-headed, in allusion to the autostylic skull 

 and the dipnoi, or lung-fishes. 



The holocephali are represented by the chim- 

 eras. These bear a great resemblance to the 

 sharks, having the body covered with placoid 

 scales. But there is but a single gill-opening 

 covered by a fold of skin. 



The dipnoi are the lung-fishes. Herein the 

 body is covered with overlapping scales, resemb- 

 ling those of the Teleostomi, and the gill-opening 

 is protected by a bony shield. 



We may express these relationships briefly as 

 follows : — 



Class Pisces. 

 Branch A. 



Hyostylic. 

 Sub-class I. Elasmobranchii. 

 „ II. Teleostomi. 



Branch B. 



Autostylic. 

 Sub-class III. Holocephali 

 „ IV. Dipnoi. 



This is the classification of Dr A. S. Wood- 

 ward, one of our greatest authorities on this 

 subject. 



