48 NATURAL HISTORY. 



SIXTH ORDER. 

 PLECTOGNATHI OR BULLET FISH. 



This order is distinguished by the globular form of 

 their bodies, and is divided into two families, one of which 

 is easily recognized by being clothed in a kind of mail ; 

 the other is smooth-skinned. 



The Moon Fish or Cephalus (orthragiscus mola) has 

 a tail so short and so high vertically that it looks as if 

 the head was cut off. It is without scales, but rough- 

 skinned ; the color is shepherd's gray ; has no fins, and 

 being so large and unshapely, as its weight is often a 

 hundred pounds, it resembles a floating millstone to which 

 it has been compared. Its flesh is very white, but in 

 boiling dissolves like lime, and has an unpleasant taste. 

 The fat is used as train oil. 



The Porcupine Fish (diodon hystrix) is cylindrical, 

 about one foot in length, and covered with spines or 

 prickles, and if excited, has the faculty of swelling itself 

 up like a balloon by swallowing air, and when the skin 

 is thus distended, the spines, with which it is armed, 

 become everywhere erect and bristle over the whole 

 surface of the body. These fishes assume this appear- 

 ance when taken by hook and line, and understand how 

 to use these weapons of Nature's providing as means of 

 defense. They are found in the neighborhood of the 

 Antilles. 



The Petrodon (petrodon hispidus), plate 20, fig. 7, is 

 one foot and a half in length, of a blue-gray color, with 

 spots of lighter shade, has four stripes of brown on the 

 sides, and four transverse bars of blue. It has the 

 power of inflating itself like the diadon, and wounding 



