64 
ROOM XI. position. The Diodons (. Diodon ) have both jaws undi- 
Nat. Hist, vided, and their skin armed with large spines. The skin 
of some species of this genus is used as a kind of helmet 
by the Chinese. 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 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 family of 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, accord¬ 
ing to the structure of their outer covering. The true 
File Fish ( Batistes ) 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 ( Monacanthus ), have the skin covered with small, 
hairy scales, and the first dorsal fin has only one spine. 
The Three-spined File Fish ( Friacanthus) has a silvery 
skin covered with small scales, and a ventral fin, con¬ 
sisting of a single spine, on each side. 
The Trunk Fish ( Ostracion ) has the same elongated 
form as the Three-spined File Fish, and the body 
covered with an inflexible case formed of regular bony 
compartments. It has a very large liver, which yields a 
considerable quantity of oil, but very little flesh. The 
body is often armed with spines, and according to its 
form, and the position of the latter, the species have 
been distinguished. 
The 
