89 
Several of these have the faculty of dilating room xl 
their stomach with air, giving the body the ap¬ 
pearance of a balloon. When this takes place 
they float along the surface of the water, belly 
upwards. Some of them, as the Diodons, have 
both jaws undivided, and the skin armed with 
large spines. The skin of some species of this 
genus is used as a kind of helmet by the Chi¬ 
nese ; others, as the Tetraodons, have the jaws 
divided in the centre by a perpendicular suture, 
and the skin covered with small slightly promi¬ 
nent spines. The Triodons have the skin of 
the Tetraodons, but the upper jaw alone is di¬ 
vided, so that they appear to have three teeth. 
The Moon Fish, or Molae ( Orthagoriscus\ 
have the same kind of jaws as the Diodons, but 
their body is compressed and without spines, 
and not susceptible of being inflated; and their 
tail is so short and high, that they have the ap¬ 
pearance of being merely the head of a larger 
fish. 
The family of File Fishes ( Balistidce ) have 
their jaws armed with a small number of distinct 
teeth; their skin is hard, and their head pro¬ 
duced, ending in a small mouth. They are 
divided into several genera, according to the 
structure of their outer covering. The true 
File Fish (. Balistes ) have a compressed body, 
covered with hard scales and spinous rays to 
the first dorsal fin; their colours are brilliant, 
and 
