THE TRUE FISHES. 193 
Porcupine-Fishes (Zetradontide).—These fishes are 
often covered with sharp spines, and when removed from 
the water they inflate themselves with air, resembling an 
oval, spiny balloon.* Each jaw is divided in the middle, 
so that they appear to have four teeth. The diodons are 
allied forms. 
Sunfishes + (Orthagoriscidz).—These are oval or ob- 
long in shape (Fig. 236). The dorsal and anal fins are 
Fic. 236.—Sunfish (Orthagoriscus mola). 
* They are often figured in this shape, but it is unnatural, and 
only attained when the fish is forcibly taken from the water. The 
Diodon antennatus has undivided, teeth-like mandibles, so power- 
ful that when swallowed by a shark they have been known, accord- 
ing to Darwin, to eat their way out through the stomach and skin. of 
the fish. 
+ They are sluggish fishes, rolling along at the surface, and are 
quite common oni the eastern coast of the United States and in 
other seas. The body is covered with a thick mucus and infested 
by parasites, goose-barna¢les even living in its mouth. Semper and 
Cobbold refer to its luminous qualities. They attain a height of six 
feet, and weigh five or six hundred pounds. The liver alone is 
valuable. 
