86 A Guide to the Zoological Collections 



We have next to consider, but more briefly, certain 

 Orders of fishes that are not represented in India. They 

 are the Ganoids and the Dipnoi. 



Ganoid Fishes [Cases 26-29]. 



To the Order of Ganoids " belong- the majority of the 

 fossil fish-remains of palaeozoic and mesozoic age, whilst 

 it is very scantily represented in the recent fauna and 

 evidently verging - on total extinction." [Gunther). 



Most of the Ganoids live in fresh water ; some species 

 of Sturgeons alone are found in the sea, but even they 

 ascend rivers at the spawning season. Their Geographi- 

 cal Distribution is shown in the coloured map in Case 29, 

 from which it will be seen that none occur in India, al- 

 though some are found in Central Asia and China. 



The Ganoids are, in a way, intermediate between the 

 Bony-fishes and the Chondropterygii. As in the Sharks, 

 the intestine has a spiral valve, though it may be rudi- 

 mentary; the bulb of the aorta is muscular, and is pro- 

 vided with numerous valves; and the tail is commonly, 

 though not always, heterocercal. As in the Bony-fishes, 

 the gills are free and lie in a common gill-chamber on 

 each side of the head — the gill-chamber being protected 

 by a gill-cover and communicating with the exterior by a 

 single opening. As in many Physostomous Bony-fishes, 

 there is an air-bladder with a pneumatic duct. The 

 skeleton may be cartilaginous and of the Chimcera type, 

 or it may be bony. There are vertical and paired fins, 

 and the ventral fins, when present, are placed far behind 

 the pectorals. The scales may be either cycloid or ganoid. 



The specimens in Cases 26-29 are merely meant to 

 give a general idea of the Order. Accipenser comes 

 nearest to the Chimaeras, Amia comes nearest to the 

 Bony-fishes. 



