ROOM XI.] NATURAL HISTORY. 49 
placed at the base of a prominent muzzle. The ventral fin 
of some of the species of this genus is very large and ex¬ 
panded, whence their name. 
The following fishes differ from all the former by the 
jaws being formed of the maxillary and intermaxillary 
bones united together into one body; and by the palatine 
arch being connected with the cranium by a suture, and con¬ 
sequently immoveable. Their skeleton is soft, but fibrous. 
Cases 7 and 8. The first of these, the Gymnodontes, 
have the jaws shaped like the beak of a parrot, and com¬ 
posed of parallel laminae united together. They live on 
Crustacea, shells, and sea-weeds, and their flesh, which 
has usually a musky odour, is said to be deleterious at 
particular seasons. Several of these fishes have the faculty 
of dilating their stomach with air, giving the body the 
appearance of a balloon. When this takes place they float 
along the surface of the water, in an inverted position. 
The Diodons ( Diodon ) have both jaws undivided, and 
the skin armed with large spines. The skin of some 
species of this genus is said to be used as a kind of helmet 
by the natives of the north-west coast of America. The 
Tetrodons ( Tetraodon ), have the jaws divided in the 
centre by a perpendicular suture, and the skin covered with 
small, slightly prominent spines. The Triodons ( Triodon), 
have the skin of the Tetrodons, but the upper jaw alone 
is divided, so that they appear to have three teeth. 
The Moon Fishes, or Molse ( Orthagoriscus ), have the 
same kind of jaws as the Diodons, but the body is com¬ 
pressed and without spines, and not susceptible of being 
inflated, and the tail is so short and high, that they have the 
appearance of being merely the head of a larger fish. 
The File Fishes ( Balistidce ) have their jaws armed 
with a small number of distinct teeth ; their skin is 
hard, and their head produced, ending in a small mouth. 
They are divided into several genera, according to 
the structure of their outer covering. The true File 
Fish ( Balistes ) has a compressed body, covered with hard 
scales, and the first dorsal fin has spinous rays; its 
colours are brilliant, but its flesh is said to be unwholesome. 
It is chiefly found in the Torrid Zone, living upon sea¬ 
weeds. Others, as the Unicorn File Fish ( Monaccinthus ), 
have the skin covered with small, hairy scales, and the 
D 
