328 



ri&uiss. 



The genera Tetraodon ana Diodon have the faculty of blowing 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. oblonyus, 

 the Oblong Sun-fish — are found in the British seas. 



Triodon. — These 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. 



Sclerodermi (Fishes 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. 



Monacanthus— 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. 



Flf. lit.— Balistes pencihigeroi. 



