328 
PISCES. 
The genera Tetraodon and Diodon have the faculty of blovring themselves up like balloons, by filling 
with air a thin and extensile membranous sac, which adheres to the peritoneum the whole length of 
the abdomen. When thus inflated, they roll over and float with the belly uppermost, without any 
power of directing their course ; but they are remarkably well defended by spines all over the surface, 
which are erected as they are inflated. Their air-bladder has two lobes. They have but three gill- 
arches in a side ; and when taken, the escape of the air from the pouch makes a sound. Each nostril 
is furnished with a double fleshy tentaculum. 
Diodon, Spinous Globe-fishes, get the generic name from the jaws consisting of only two pieces, one above and 
the other below. Behind the trenchant edge of each piece, there is a rounded portion furrowed across, and 
forming a powerful grinding apparatus. The spines upon the inflated skin, which vary a good deal in the dif- 
ferent species, present a formidable appearance. They inhabit the warm seas; but sometimes, though rarely, a 
specimen, brought no doubt by the Atlantic current, is found on the coast of Cornwall. 
Tetraodon, have each jaw marked with a suture, so as to give the appearance of four teeth. The spines are 
small and low, and some species are reckoned poisonous. None of them is recorded as visiting Britain. One is 
electrical, T. lineatus, straight, brown and whitish ; it is found in the Nile, cast on shore by the inundations, and 
collected by the children as a plaything. 
Orthagoriscus, the Sun-fish, has the body compressed, spineless, and incapable of inflation, with the tail so short 
that it appears only the anterior half of a fish which had been cut in two in the middle. Their dorsal and anal, 
both high and pointed, are united to the caudal ; no air-bladder, and the stomach is small ; their surface is covered 
with mucus. They are found in many seas ; and two species at least — 0. mola, the Short Sun-fish, and 0. oblongus, 
the Oblong Sun-fish— are found in the British seas. 
Triodon.—T\\QS,e species have the mark of a suture on the upper jaw, but none on the under, which gives them 
the appearance of having three teeth. A vast membrane, as long as the body, and twice as high, is supported 
before by a large bone answering to the pelvis, and makes these fishes resemble Balistes, in the following family. 
Fins as in Diodon, body rough like Tetraodon, and the surface of the membrane roughened by a number of little 
oblique crests. The only known species is from the Indian Ocean. 
THE SECOND FAMILY OF THE PLECTOGNATHI. 
SciiERODERMi (Fishcs With Hard or Granulated Skins). 
These are readily distinguished by a conical or pyramidical muzzle, which is prolonged forwards from 
the eyes, and terminates in the mouth, with distinct teeth in both jaws. The skin is either rough or 
covered with very hard scales; and the air-bladder is large, strong, and of an oval shape. There are 
two genera. Balistes, File-fishes, admit of subdivision, and have the body compressed ; eight teeth, 
generally trenchant, in a single row in each jaw ; the skins scaly or granulated, but not osseous ; the 
first dorsal composed of one or more spines, articulated with a particular bone, which is attached to 
the cranium, where is a groove for its reception ; the second dorsal and anal long, and placed opposite 
each other. Though without ventral fins, they have pelvic bones attached to the shoulders. They 
abound in the warm seas near rocks, or on the surface of the water ; and their brilliant colours sparkle 
in the water like those of Chetodons. Their flesh is disliked at all times ; and they are supposed to 
feed on Coralline Polypi at some seasons, and become poisonous, but Cuvier found only sea-weed in 
such as he opened. 
Balistes proper, have the whole body covered with long and hard rhomboidal scales, which do not overlap each 
other, but have the appearance of the teeth of a file ; three 
spines on the dorsal, the first long, the third small and far 
back; extremity of the chest salient and prickly, with 
some spines in the skin behind, which have been con- 
sidered as rays of ventral fins. Some have no particular 
armature of the tail ; and of these, again, some have large 
scales behind the gill-openings. Such is the European 
File-fish — B. capriscus, which has been occasionally, but 
very rarely, found on the British shores, and which is com- 
mon in the Mediterranean. 
Mo7iacanthus.— This subgenus has very small scales, set 
rough like the pile of velvet ; a large cirrated spine on the 
first dorsal, and the extremity of the pelvis salient and 
spinous. Some have the pelvic bone moveable, and con- 
nected with the abdomen by an extensile membrane, and 
frequently strong spines on the sides of the tail. Some have 
stout bristles on the tail, some have the body with tuber- 
cles, and others with branched hairs. 
