56

FILE-FISH.-TRUNK-FISH.

the surface, or in the neighbourhood of rocks. Some of them are remarkable for the appendages with which the body is

furnished, which are

especially striking in the Balistes pencilli

gerus; their use, however, is entirely unknown.-The Ostracions, or Trunk-fishes, should probably be placed in a a distinct family, so remarkably are they distinguished by the mode in whch the body is protected.

The head and body are covered with plates of bone, soldered together in such a manner as to form an inflexible cuirass; leaving only the tail, the

fins, the mouth, and a small margin of the gill-opening, capable of motion,-all of which moveable parts pass through openings of the cuirass. The greater part of the vertebræ also are

soldered together. There are no ventral fins, and the dorsal and anal are small and are placed far back; there is little flesh; but the liver is large, and abounds in oil. The surface is often armed with spines. No species of these singular Fish are known in the British seas.

ORDER VII.-CHONDROPTERYGII BRANCHIIS

LIBERIS.

581. We are now arrived at the true Cartilaginous fishes (§ 525); of which the first order so far resembles the Osseous group, that the gills are connected externally with a single wide opening on each side, furnished with an operculum, or gill-cover. All the Fishes of this order are considered by Cuvier as belonging to a single family; but they may be probably better arranged under two families, the ACIPENSERIDE, or Sturgeons, and the CHIMERIDE, or Chimaras,-the former having more affinity to the Osseous fishes, and the latter to the Sharks. The body of the Sturgeon is more or less covered with bony plates,

FIG. 280.-STURGEON.

arranged in longitudinal rows; and the head is armed with the same. The mouth is situated beneath the elongated muzzle, and is small and toothless. The air-bladder is very large, and communicates by a wide opening with the gullet; and in this, and other points of their internal conformation, the Sturgeons show a considerable approach to the Lizards, whence they are ranked among the Sauroid fishes (§ 588). The form of the tail is another mark of resemblance; for the vertebral column is continued into the upper portion of the caudal fin, the lower one being given off from its underside,-instead of stopping short at its commencement, and sending off the upper and lower portions of the fin in the same manner, as in nearly all other Fishes (Fig. 246). Sturgeons, like Salmon, ascend large rivers for the purpose of spawning; and they are the subject of valuable fisheries. They are more abundant in the Continental rivers than in those of Britain; and are particularly numerous in those

58

STURGEONS.-CHIMÆRIDÆ.-SHARKS, ETC.

which fall into the Black and Caspian seas. The common Sturgeon attains the length of six feet; but the great Sturgeon has been found twelve or even fifteen feet in length, and weighing from 1200 to 3000 lbs. The flesh of the former is very palatable and wholesome, resembling veal in its character; that of the latter, however, is not esteemed. The Sterlet is a smaller species, about two feet long; which is found in the Russian rivers, and is considered a great delicacy. All the species are valued on account of the excellent Isinglass which is yielded by their air-bladders; and their roe is salted, and prepared by the Russians, forming a dish termed caviare. More than 400,000 lbs. of this have been prepared in the Caspian fishery, in a single year. The CHIMERIDE have the gills not entirely free at their extremities, but partly attached, as in the Sharks; and although there is externally but a single gill-opening, yet internally there are five separate passages, terminating in the common aperture. They lay large, flattened, eggs, included in a sort of leathery covering; in which respect, also, they resemble the Sharks. The commonest species is known under the name of the "King of the Herrings."

ORDER VIII.-CHONDROPTERYGII BRANCHIIS FIXIS.

582. This order includes the two families of Sharks and Rays; which, though very different in external form, agree in many points of internal structure, and particularly in having the gills fixed at their extremities to the outer sides of the gill-cavity, and in having a series of apertures, through which the water passes out from each branchial arch. In these particulars they correspond with the last order of the class,-that of Cyclostome Fishes; but they differ from them in having a much more perfect skeleton, and in having both pectoral and ventral fins. The differences between the two families of SQUALIDE, or the Shark tribe, and RAIDE, or the Ray tribe, chiefly consist in their external form; the body in the former being elongated, and the

WHITE-SHARK; FOX-SHARK.

59

tail extremely fleshy; whilst in the latter the body is short and flat, the pectoral fins immensely extended, and the tail slender. Of the true Sharks, there are several species, of which the White

shark is the most notorious.

It sometimes attains the length of twenty feet, and its mouth is sufficiently wide to enable it to receive the thigh or even the body of a Man. This species inhabits most of the seas of warm latitudes; but it is rarely or never seen near our own shores. The Fox-shark, or Thresher, is

FIG. 282.-FOX-SHARK.

remarkable for the great development of the upper lobe of the caudal fin, into which the vertebral column is prolonged (§ 581); this being nearly as long as the entire body. This fish is occasionally met with on our own coasts, and sometimes attains the entire

60

THRESHER, BLUE-SHARK, PORBEAGLE, DOG-FISH.

length of from ten to twelve feet. Its gape is not so wide, nor are its teeth so formidable in proportion to its size, as those of the preceding; but its tail is a powerful weapon, and it is exceedingly bold and voracious in its disposition. It has been stated on good authority, that it is not uncommon for a Thresher to approach a herd of Dolphins which may be sporting in unsuspicious security, and by one splash of its tail to put them all to flight, like so many hares before a hound; yet the Dolphin is six times the bulk of the Thresher.-The Blue-shark bears more resemblance to the White in its general form, but is much smaller, not exceeding six or seven feet in length. It is very common off the Cornish coast, and is extremely troublesome to the fishermen during the Pilchard-fishing season, cutting their lines and nets, and devouring the fish.-The Porbeagle belongs to an allied genus, Lamna, which differs from the true Sharks in having a pyramidal snout, and the gill-openings placed rather further forwards. Its common name seems to be compounded of Porpoise and Beagle; for it bears some resemblance to the former in shape, whilst it corresponds with the latter in its babit of hunting in packs. It is occasionally met with on almost all parts of the British coasts, being found chiefly in currents near rocky places; it is voracious in its habits, swallowing entire Fishes of two feet in length.-The Notidamus, which is an inhabitant of the Mediterranean, is the largest of the true Fishes, its length being sometimes as much as thirty-six feet; but it is comparatively harmless.

583. This family contains many other genera, more or less departing from the ordinary type; among these we may mention the curious Zygana or Hammer-headed Shark; which resembles the ordinary Sharks in the form of its body, but has its snout prolonged into the form of a double-headed hammer, with an eye in the middle of each extremity. It is occasionally met. with in European seas, attaining the length of twelve feet, and larger ones are said to inhabit the tropical ocean.— The Dog-fish is nearly allied to the Sharks; and is probably more abundant on our own coast than any other of the order. Almost every one who walks along the shore may meet with its