G90 



ICHTHYOLOGY. 



ClassiBca- it as our opinion, that the organs of respiration furnish 

 tion of characters which are obvious, permanent, and natural, 

 means of these characters, fishes may be divided in- 

 to two great classes, viz. those withjucetl and those with 

 free gills; and the inferior divisions might depend on 

 circumstances connected with the number, position, 

 and structure of the accessory organs. But instead of 

 attempting, in this place, to give a new system of ich- 

 thyology, we propose to lay before our readers a con- 

 densed view of the genera according to the system of 

 La Cepcde, the outlines of which have been already 

 given in the historical part of this article. We propose 

 to add occasional observations on the characters of these 

 genera, and on the history of rare or useful species. In 

 the account of species it is necessary to be concise, as 

 an enumeration of all the known species of fishes, 

 amounting to upwards of 1470, would swell the article 

 to an inconvenient length. 



SUB-CLASS I. CARTILAGINOUS FISHES. 



Cartilagi- IN the fishes belonging to this sub-class, the skeleton 

 rious fishes, never becomes so much indurated as to deserve the 

 name of bone, but continues in the form of cartilage 

 more or less compact. As this internal character can- 

 not be discovered without the use of the dissecting 

 knife, its employment in the formation of the pri- 

 mary divisions of a systematic arrangement has been 

 justly condemned by many naturalists, and ought to be 

 relinquished. The genera which are included under this 

 division, exhibit great differences in the structure of 

 their organs of respiration and reproduction. 



DIVISION I. 



THE cartilaginous fishes of this division are destitute 

 of a gill lid and gill flap. The gills are likewise fixed. 



ORDER I. APODAL. No ventral Fins. 



The structure of the animals of this very natural or- 

 der has been ably investigated by Sir Everard Home, 

 as we have already pointed out, while describing the 

 organs of respiration and reproduction. They consti- 

 tute the last link in the chain of fishes, and form the 

 transition to the molluscous animals. 



GENUS I. PETKOMYZON. Lamprey. 



Lamprey. Seven gill-openings on each side of the neck, and 

 an aperture on the top of the head. 



The species of this genus possess an organ of adhe- 

 sion on the lips, by which they attach themselves to 

 stones ; hence the name Petromyzon, from mr^, lapis, 

 nnd ft.v%au, sugo. Lacepede enumerates nine species, 

 three of which are British. They are distinguished by 

 characters drawn from the form of the dorsal and cau- 

 dal fins. All the species are vivacious, and may be kept 

 in life for a considerable time when out of the water. 

 The P. Planeri, found in the rivulets of Thuringia, 

 when plunged into diluted alcohol, will survive up- 

 wards of a quarter of an hour ; but it indicates, by its 

 convulsive movements, the painful effects produced by 

 the fluid on its organs of respiration. Some of the spe- 

 cies are used as food, but principally for baits. 



GENUS II. GASTIIOBHANCHUS. Has. 



& 



Hag. Gill-openings, two in number, situated under the belly. 



This genus was formed by Blocli from the Myxine 



glutinosa of Linnaeus. Tiiis last author placed it among 



his Vermes intestina ; and the former, upon restoring it Classifies. 

 to its proper place among fishes, bestowed upon it a tl n ot 

 new name. Only two species are known. '^'^i"*!!/ 



ORDER IV. ABDOMINAL. 



This is a very natural order. The species are ovovi- 

 viparous, and are distributed by Lacepede into tliree 

 genera. 



GENUS III. RAIA. Ray. 



Body depressed, five gill-openings on each side placed Roy- 

 beneath, mouth under the snout. 



This is a very extensive genus, including, according 

 to La Cepede, thirty-six species. Some naturalists 

 however, are disposed to regard a few of these as hy- 

 brid animals. Several new genera have been separated 

 from it, particularly the genus CEPHALOPTEKUS, which 

 includes those species with a divided snout, and the 

 torpedo, the characters of which we shall shortly notice. 

 The species have been divided into several section?, 

 from the form of the teeth, and the spines on the body; 

 but the observations of Montagu appear to indicate 

 these characters, as pointing out the differences of the 

 sexes, not as sure marks by which the species may be 

 distinguished. His remarks on this subject we have 

 already stated under the head of reproduction. Many 

 of the animals of this genus grow to a large size. They 

 furnish a wholesome and palatable food, and are used 

 either when fresh, salted, or dried. The spines of some 

 are considered by the fishermen as venomous. One 

 species, the R. Sephen of La Cepede furnishes, accord- 

 ing to this author, the well known article of commerce 

 termed shark's skin, or shagreen. This skin is covered 

 with round hard tubercles, and, when dressed, is used 

 to cover boxes or cases. The squalus canicula furnishes 

 an inferior sort of skin, which is often used as a substi- 

 tute, but the tubercles are smaller; and not so regular 

 in shape. 



GENUS IV. TORPEDO. Cramp-Fish. 



Body smooth, depressed, and obtuse before ; five Cramp-fish, 

 gill-openings on each side, placed beneath ; electrical 

 organs single on each side. 



This genus, which has been lately revived, contains 

 at present four species according to Ilisso ; but the cha- 

 racters which separate them are far from being deter- 

 minate. The best known species is the Raia torpedo 

 of Linnaeus, whose electrical organs have been already 

 described under the article ELECTRICITY of this work. 



GENUS V. SQUALUS. Shark. 



Body round, tapering ; gill openings from five to Sharks, 

 seven on each side of the neck. 



This genus contains upwards of thirty species, whose 

 characters and organs have not been described with 

 sufficient attention. They exhibit very obvious differ- 

 ences in the structure of their organs of respiration, 

 and on that account ought to be separated into several 

 genera. The characters furnished by the organs of 

 motion should be employed in forming the genera into 

 sections. 



The sharks are voracious and formidable ; they pos- 

 sess great strength, and swim with considerable veloci- 

 ty. The smaller species are salted and dried, and used 

 as food. The liver yields a considerable quantity of 

 oil, and the skin of some species is used, on account of 

 its roughness, to polish wood, brass, or ivory. It is 

 likewise employed to make thongs and tackle for car- 



