BONY FISHES AND GANOIDS. 



489 



Fig. 19. COFFEE-FISH. 



The first family of the Plectogathi is represented by the file-fishes 

 (Batistes, etc.) and the strange coffer-fishes (Ostracium). In these fishes there 

 are a few separate teeth in the jaws, and traces of the spinous 

 dorsal and pelvic fins usually persist. In form, the body Family 



may be either compressed or angulated, and the muzzle is Balistidce. 

 rather elongated ; the skin being either spiny or rough, or 

 replaced by a bony armour. Their chief habitat is the tropical oceans, al- 

 though some range into cooler seas. The Oriental genus Triacanthus belongs 

 to a sub-family characterised by the 

 presence of roughened scale-like plates 

 on the skin, and the retention of from 

 four to six spines in the first dorsal 

 fin. On the other hand, Batistes is 

 included in a sub-family in which 

 there are never more than three spines 

 in the fin last mentioned ; while the pelvic fins are absent, or indicated only 

 by a swelling on the lower surface of the body ; the compressed body being 

 clothed with scale-like plates capable of being moved, or with a roughened 

 skin. There are several genera in this group, and the flesh of certain kinds 

 is poisonous. Batistes itself, which is furnished with powerful cutting teeth 

 in the front of the jaws, browses upon living coral, or eats through the shells 

 of molluscs in order to get at the animal within. The angulated bony cara- 

 pace composed of hexagonal plates joined together like mosaic sufficiently 

 distinguishes the coffer-fishes (Ostracium), which constitute a sub-family by 

 themselves. 



The second family includes the globe-fishes and their near allies the sun- 

 fishes, in both of which the bones of the jaws are welded together so as to 

 form a cutting parrot-like beak of great power. The teeth 

 are modified into large dental plates tightly adherent to the Family 



jaws, and consisting structurally of a number of very thin J)iodontidce. 

 parallel laminae, arranged like the leaves in a book. These 

 fishes are mostly inhabitants of the hotter seas, although a few have taken to a 

 fresh -water existence. The one Oriental species of Tfiodon alone represents 

 the first sub-family, and has the skin of the lower surface dilated into a large, 

 inflatable sac ; the dental plate of the upper-jaw being divided in the middle, 



while that of the lower is single. 

 Spiny bony plates, which do not over- 

 lap, clothe the body, and the tail-fin is 

 forked. The globe-fishes (Diodon, 

 Tetrodon, etc.) form the second sub- . 

 family, and have the more or less 

 shortened and rounded body covered 

 with spines, while there is a distinct 

 tail and caudal fin, and the distensible 

 throat can be inflated with air. The 

 different genera are chiefly distin- 

 guished from one another by the con- 

 formation of the dental plates, and the size and distribution of the spines. 

 Dr. Giinther writes, that " these fishes have the power of inflating their body 

 by filling their distensible oesophagus with air, and thus assume a more or 

 less globular form. The skin is then stretched to its utmost extent, and the 

 spines protrude and form a more or less formidable defensive armour, as in a 



Fig. 20. GLOBE-FISH. 



