PLECTOGNATHI. 233 



Two of the genera, Tetraodon and Diodon, have the faculty of 

 swelling themselves up like a balloon, by filling their stomach (or 

 rather a sort of very thin and extensible crop, which occupies the- 

 whole length of the abdomen, and adheres closely to the peritoneum, 

 a circumstance which has occasioned it to be considered at one 

 time as the peritoneum itself, and at another as a species of epi- 

 ploon) with air. When thus inflated, they roll over, and float on the 

 surface, with the abdomen upwards, unable to direct their course; 

 but they are extremely well defended while in this position by the 

 erection of the spines with which their skin is everywhere furnished. 



DIODON, Lin. 



So called because the jaws are undivided and formed of one piece above 

 and another below. Behind the trenchant edge of each of these pieces, is. 

 a round portion, transversely furrowed, which constitutes a powerful instru- 

 ment of mastication. The skin is everywhere so armed with stout pointed 

 spines, that when inflated, they resemble the burr of a chestnut tree. A 

 number of species inhabit the seas of hot climates. 



TETRAODON, Lin. 



Jaws divided in the middle by a suture, so as present the appearance of 

 four teeth, two above and two below; spines small and low. Several spe- 

 cies are said to be poisonous. 



CEPHALUS, Sh. 



Jaws undivided as in Diodon; but the body, compressed and spineless, is 

 not susceptible of inflation, and the tail is so short and high that this fish 

 resembles one whose posterior portion has been truncated, producing 1 a 

 singular appearance, that is amply sufficient to distinguish it. A thick layer 

 of a gelatinous substance is spread under the skin. 



(7. brevis, Sh. (The Short Sunfish.) Four feet and more in length, 

 and weighing upwards of three hundred pounds; the skin is very rough, and 

 of a fine silver colour. European seas. 



TEIODON, Cuv. 



We also make a separate genus of these, fishes, whose upper jaw is divid- 

 ed as in Tetraodon, and the lower one single, as in Diodon. An enormous 

 dewlap almost as long as the body and twice as high, is supported before 

 by a very large bone which represents the pelvis and approximates them 

 to certain Balistes. Their fins are those of a Diodon, their body is rough 

 as in Tetraodon, and the surface of their dewlap is covered with numerous, 

 small, rough crests, placed obliquely. 



T. bursarius, Reinw. The only species known; it was discovered in the 

 Indian Ocean by M. Reinward. 

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