CHAPTEK II. 



ON CLASSIFICATION. 



The Fishes form one of the Great Classes of the 

 Animal Kingdom. 



They are divided by the latest authors, first into six 

 Sub- Classes, as follows : — 



I. Teleostei, or fishes with a complete bony skele- 

 ton, which includes all the most perfectly organised 

 forms ; by far the greater number of existing fishes 

 are included in this sub-class, among them all the 

 species that we are concerned with in this book. 



II. Dipnoi, of which only two species are known. 



III. Ganoidei, in which are the sturgeons, and a 

 few other forms. 



IV. Chondropterygii. Fishes with a cartilaginous 

 skeleton, which includes all the sharks and rays. 



V. Cyclostomata. " Bound-mouthed," or sucking- 

 fishes, including the lampreys and their allies. 



YI. Leptocardii. Only one species known. 



