266' ZOOLOGY. 



there is a thick opaque membrane, covering the belly 

 of the fish ; and this, when distended with air, pro- 

 duces the inflated appearance of the body. It can be 

 distended or emptied at the option of the animal, and is 

 evidently supplied with air through the mouth and 

 throat; although I was unable to detect the precise 

 point of communication.* I noticed, however, that by 

 blowing into the mouth of the dead fish, I could inflate 

 this membrane, and by passing a finger into the throat 

 could as readily empty it. 



To produce the inflation of the body, (which must 

 be regarded as a mode of defence,) it would appear that 

 the fish should have access to atmospheric air. Two 

 nostrils, provided with broad fleshy margins, at the 

 extremity of the snout, may supply this want when 

 the fish is on the surface of the sea, and it is question- 

 able whether water may not be employed as a substitute 

 for air in the ocean's depths. 



THE FIVE-SPINED TRUNK-FISH. 

 (Ostracion Pentacornis, N. Sp.) 



Entire length one inch ; body quadrangular ; belly 

 broader than the back ; plates of the armour hexagonal, 

 tuberculated on the sides and back, smooth on the 

 abdomen ; mouth small and orbicular : snout promi- 

 nent ; one straight spine over each eye, one on each 

 side the tail, and a fifth, solitary and recurved, near 

 the centre of the back. Colour of the sides and back 

 deep-blue, spangled with small sapphire-coloured spots ; 

 abdomen white ; iris silvery. 



This small Trunk- fish is very pelagic in its habits. 

 We obtained examples only on the surface of the 

 deepest waters of the Pacific, far from land, and in the 

 greatest abundance in lat. 27 N. 



* It is usually an opening in the gullet. 



