146 
NATURAL HISTORY. 
[n. ZOOL. GAL. 
and covered with the skin, leaving merely a small tubular opening for 
the emission of the water. This structure enables the fish to live a long 
time out of water. They have been divided into several genera, ac¬ 
cording to the teeth and the proportion of the fins. In most of the 
species, the dorsal and anal fins are long and united together; in others 
they are short and quite separate ( Moringua ); and in some they are 
entirely wanting. In one genus ( Synbranchus ), the gill-flaps only 
open by a single aperture in the under side of the neck. 
The Gymnoti ( Gymnotidje) have the gill-flap covered with a mem¬ 
brane, like the Eels; but this membrane is open behind the pectoral 
fins. These fishes have no dorsal, but a long anal fin. In some the 
body is eel-shaped and naked, as in the Electric Gymnotus ( Gymnotus 
electricus'). In the Carapi ( Carapi ) the body is compressed and co¬ 
vered with scales. The Gymnarchi ( Gymnarchi ) differ from the 
Carapi merely in having a long dorsal, and no anal fin. The Morris 
( Leptocephalus ) is very peculiar for the exceeding thinness of its body, 
which resembles a riband, and is nearly as transparent as glass ; its fins 
are scarcely visible, and its intestines occupy merely a very narrow line 
along the lower edge of the body. 
The Launces ( Ammodytes ) have elongated, compressed bodies, 
covered with scales placed in transverse series, and the dorsal, caudal, 
and anal fin separate from each other. The jaws are acute and exten¬ 
sile : they bury in the sand and live on the worms which they find in it. 
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 consequently immoveable. Their skeleton is soft but 
fibrous. 
The first of these, the Gymnodontes (or Diodontidje) have 
the jaws shaped like the beak of a parrot, and composed 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 (Dio- 
don ) 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 Tetro- 
dons ( 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, hut the upper 
jaw alone is divided, so that they appear to have three teeth. 
The Moon Fish, or Molse ( Orthagoriscus ), have the same kind of 
jaws as the Diodons, but the body is compressed 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 (Balisthle) 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, ac- 
