PLECTOGNATHI. 223 



DIODON, Linnaeus, 



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 instrument 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, LIHTUEUS. 



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

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

 are said to be poisonous. 



CEPHALUS, Shaw. 



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 a singular appear- 

 ance, that is amply sufficient to distinguish it. A thick layer of a gelatinous 

 substance is spread under the skin. 



C. 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. It is found in the European seas. 



THIODON, Cuvier. 



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

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

 lap, almost as long as the bcdy, 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 Tetra- 

 odon, 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. 



