CHAPTER 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. 
IY. Ciiondropterygii. Fishes with a cartilaginous 
skeleton, which includes all the sharks and rays. 
Y. Cyclostomata. “ Round-mouthed,” or sucking- 
fishes, including the lampreys and their allies. 
YI. Leptocardii. Only one species known. 
