283 



XXIY. FAMILY WITH NAKED TEETH. 

 GYMNODONTIDiE. 



Rp-jjresentatives in British Fauna. — Gen. 2, Sp. 3. 



Gen. IOO.Tetrodon. Sp.210. T.PewTtanfw. Pennant's Globe- 

 fish. 

 101. Orthagoriscus. 211.0- ttioIcu . Short Sun-fish. 

 212. 0. oblongm. Oblong Sun-fish, 



Gen. C. Tetrodon. — In the absence of true teeth, 

 the partially exposed jaws are divided in the middle 

 by a suture, thus presenting the appearance of four 

 teeth, as the name implies. The species are, pro- 

 perly speaking, tropical; and in common with 

 those of the genus Diodon, which has no represen- 

 tatives in Britain, they possess the singular power of 

 inflating the belly into a rounded ball by swallow- 

 ing air. When thus inflated, in consequence of the 

 under parts becoming lighter than the upper, they 

 turn upside down, and continue to float about in this 

 position, apparently retaining the power of direct- 

 ing their course. As the inflated abdomen is covered 

 with spines, this seems to be a means of warding 

 off* the attack of enemies ; at least there can be no 

 doubt that it is often attended with that effect, al- 

 though the occurrence of certain species with the 

 parts in question entirely smooth (Leisomus of 

 Swainson, a name inadmissible because previously 



