262 



FISHES. 



ORDER PLECTOGNATHI.* 



The chief distinctive character of these fishes is that the maxil- 

 lary is solidly fixed to the intermaxillary bone, and the whole 

 united to the cranium, so as to be immoveable. Moreover, their 

 opercula are concealed beneath a thick skin, which leaves exter- 

 nally only a small branchial slit. They have no true ventral fins. 



In the family of Grymnodonts t there are apparently no teeth, 

 but the jaws are furnished with a species of beak, internally di- 

 vided into plates, which form a grinding surface. To this family 

 belong 



The Globe-Fishes (Diodoii)& so called because their jaws being undivided 

 have each but a single tooth-like piece, and the Tetradons, in which both 

 jaws are divided in the middle, so as to present the appearance of four teeth 

 two above and two below. 





*X&-* 



FIG. 280. GLOBE FISH. 



These two genera of fishes have the faculty of swelling themselves up like 

 a balloon by swallowing air : this peculiarity has obtained for them the com- 

 mon names of " Swell-fish," " Porcupine-fish," " Balloon-fish," &c., &c., and 

 furnishes them with a means of defence, for when the skin is distended, the 

 spines with which it is armed become everywhere erect, and project from the 

 whole surface of the body ; when thus swollen, they turn over, the belly coming 

 uppermost, and thus they float on the surface of the sea. They are found in 

 tropical climates. 



The Sun-Fishes (Orthagoriscus^ Mola ^[), sometimes also called Moon- 

 fishes^ resemble the Diodon in the arrangement of their jaws, but the body is 

 compressed and of a strange shape ; it has no spines, nor is it susceptible of 



* 7rXe/cr6?, plectOS, twisted, conjoined; yvdOos, 



gnathos, the jaw. 

 *T yvfiyfa, gymnos, naked ; 656v$, 686vTOs, 



odous, odontos, a tooth. 

 + Si's, clis, double ; 6d6vs, odovros, odous-, 



odontos, a toot!*. 



rer/xz, tetra, four; 656vs, 656vTos t odous, 



odontos, a tooth. 

 || opBayopiffKos, orthagoriscos, a suking - 



P& 



"\, Mola, a mill stone. 



