ICHTHYOLOGY. 



229 



Clasaifica- («•) sub-family.— petromyzonina. 



tion — Der- (With distinct teeth and eyes.) 



mopteri. Genus f. Petromyzon. Two conical upper pharyngeal teeth 

 ^**-^V ^ close together ; a single crescentic under one ; numerous conical la- 

 bial teeth, two fringed lingual ones. P. m«ri'n»s, and four other species. 



Genus II. Lampetra. Upper and under pharyngeal -teeth 

 transversely crescentic ; labial teeth in two rows on the border of 

 the lips ; more interior lateral teeth bigger, irregularly twice or 

 thrice notched ; lingual teeth pectinate. P. fuviatilis, jilaneri, and 

 two other species. 



Genus III. Geoteia. Upper and under pharyngeal teeth 

 transversely crescentic, the upper one lobed ; labial teeth nume- 

 i-ous, remote, pointed, the interior ones the biggest; lingual teeth 

 long, conical, curved. One.species. <?. australis. 



Genus IV. Velasia. Upper and under pharyngeal teeth trans- 

 versely crescentic; the upper bilobate ; labial teeth narrow, trun- 

 cate, the interior ones the biggest; lingual teeth rather long, 

 curved. V. chitensis. 



Genus V. Caragola. Two upper, three-lobed, pharyngeal teeth, 

 widely apart ; under one crescentic, nine-lobed ; labial teeth four- 

 bundled ; lingual teeth flat. C. lapicida. 



Genus VI. Mokdacia. Two upper pharyngeal teeth ; the la- 

 teral ones trilobate ; nine under conical ones in a curved row ; 

 labial teeth conical, in a single series on the margin of the lip ; 

 Ungual teeth long, conical, curved. P. mordax. 



(b.) SUB-FAMILY. — AMMOCCETINA. 



(Without teeth and with obscure eyes.) 

 Genus VII. Ammoc<etes. Five species. 



Sub-Order III.— RIBBON ABODALS. 



These delicate, semi-transparent, and scaleless fishes are 

 inhabitants of all the oceans, and the species are probably 

 numerous, though it is only in localities where much atten- 

 tion is paid to fish that tiiey are likely to be noticed. They 

 are many, and of considerable variety of form in the 

 Mediterranean, and one species is occasionally taken by 

 keen naturalists on the English coasts. Several liave been 

 described that inhabit the Indian seas ; and on Sir James 

 Clark Ross's antarctic voyage one specimen was obtained in 

 a high southern latitude. The absence of ossification in the 

 skeleton, the gelatinous condition of the sheath of the spinal 

 marrow, which, in the form of a " chorda dorsalis," reaches 

 into the base of the skull ; and the persistence of the pri- 

 mordial cartilaginous cranium are reasons for placing these 

 fishes with the Dermopteri. 



Sub-Order III.— APODES LEMNISCATI. 



Ribbon-shaped, extremely compressed fishes. Gills free, sub- 

 operculate; no air-bladder. Skeleton cartilaginous; no scales. 

 Blood colourless ; no spleen. 



Family I.— LEPTOCEPHALID^, Bon. 



HelmicktkyidcE, Koll. Small, greatly compressed, blade-shaped, 

 apodal, diaphanous fishes, totally destitute of scales, with a late- 

 ral line formed by the intersection of the muscular layers ; some 

 have, some want teeth; and the pectoral fins are also present 

 in some species, and wanting in others. The anus is placed on 

 the ventral edge of the fish, before or behind the middle, and the 

 simple straight gut runs near the ventral edge of the fish. Their 

 skeleton is very incomplete and cartilaginous, and the myelon is 

 obscurely visible through it. In most, the anal and dorsal, uniting 

 at the end of the tail, form a pointed or blunt, but very seldom a 

 forked caudal, in which the rays are generally discoverable. 



Genus I. Esunculus, Kaup. J.eptocqdiaii with small pecto- 

 rals and a forked caudal. One species, Italy. 



Genus II. Hyprokus, Koll. Jaws straight, much elongated, 

 with merely traces of dentition. Hinder nostrils before or over 

 the eyes; muciferous pores along the jaws and round the eye. 

 Body elevated and gibbous at the occiput; tail pointed. Pectorals 

 minute ; rudimentary anus before the middle ; caudal not distinct 

 from the other vertioal fins. One species, Messina. 



Genus III. OXYSTOMUS, Rafin. (Tilnrns, KoM.) Distinguished 

 from Leplocephalus by the rayle.=s, cutaneous dorsal fin com- 

 mencing at the occiput, and by the upiior and under transverse 

 muscular bands not making an angular intei'ruption or brealc 

 anteriorly at their intersection; no anal fin; anus far back, near 



where the tail is attenuated into a longish filament. Head small ; Classifica- 



mandible a trifle longer ; pointed teeth on both jaws ; gill-openings tion Der- 



furnished with distinct opercula, and squeezed together on the mopteri. 

 throat. Three species. v ^ ^ y 



Genus IV. Leptocephalus, Lin. (Hdmichthys, Rafin.) Pis- 

 tinguislted from Oxi/stomus by none of the species having the tail 

 so prolonged into a hair-like point, and by the muscular bands 

 making a distinct angular intersection anteriorly. Some species 

 have, others want teetli ; there are species in which the teeth can be 

 seen only through a microscope, and others whose pointed teeth are ■ 



distinctly visible to the naked eye. Most have small pectorals, but 

 some show' not even a trace of these fins. At the end of the gut 

 there is an anal opening as fine as a hair, which gives exit to the 

 fluid excrement. Eighteen species. 



Genus V. Cheilobuanchus. Rich. Form compressed; body 

 linear-lanceolate. Head very small; snout obtuse; jaws equal. 

 Mouth small; teeth uniscrial, acute, becoming blunt with age, 

 closely ranged so as to form an incisorial series; lips loose. Anus 

 before the middle ; dorsal and anal mere cutaneous folds without 

 rays or interneural bones ; a single interneural at the point of the 

 tail, which supports seven or nine jointed rays; caudal united with 

 the cutaneous dorsal and anal; muscular layers forming chevrons, 

 which have the apex of the angle on the lateral line, and directed 

 forwards, as in Leptoccphahts ; abrachiul and apodal. Gill-opening 

 under the throat, a small transverse slit, common to the two sides, 

 without a division in tlie middle ; the edge of the membrane free; 

 a cutaneous fold, ending on each side in a minute lobe, forms the 

 posterior edge of the opening, and seems to be capable of acting 

 like a'valve, with the aid of an interior membranous fold; bran- 

 chiostegals three; a minute genital papilla; a single pancreatic 

 caicum was observed ; the intestine appeared to be straight, with a 

 stomachal dilatation. The skin is smooth, but minutely pitted, as 

 if from microscopical sunken scales. Vertebrae 73, ossified. Two 

 species — one obtained at Penguin Island, in Ijat. 72. S. 



Order II.— MAL.ICOPTEROUS FISHES. 



Sub-Order I.— SERPENTIFORM APODALS. 



In the Lancelets, the only representatives as yet known of 

 the order of Dermopteri, we have seen that the skeleton is 

 membranous, that the spinal nervous chord is continued to 

 the anterior end of the fish without expansion, and that in 

 conformity with this simplicity of the nervous centre, the 

 head cannot be distinguished from the body, and may be 

 said to be wanting, — the only part of the face that is deve- 

 loped being the mouth and oral filaments. In the Supkers 

 the skeleton rises from the soft membranous condition of 

 that of tlie Ammncete, to the production of a tendinous 

 spinal chord filled with gelatine, and partially encompassed 

 by cartilage ; teeth exist on the palate and lips, though as 

 yet seated only in the soft parts, and formed of indurated 

 mucoid matter; while the jaws are wanting. The group we 

 have now to speak of consists of fishes with a well ossified 

 skeleton, and a head that is at once recognised as such, but 

 with the bones of the face less fully developed than in osse- 

 ous fishes more highly organized. A single bone represents 

 the nasal, ethmoid, and vomer, or it may be said that these 

 three bones have coalesced into one, which is firm and strong. 

 The pre-maxillaries and the maxillary are wanting, the pala- 

 tines coming in contact with the lips to form the lateral 

 portions of the upper jaw, which are opposed to the man- 

 dible, — the teeth which arm these bones standing in reverse 

 order with regard to one another ; for instance, when they 

 are biserial, and the inner row is tiie tallest on the palatines, 

 the outer row of the mandibulars is the tallest, and is op- 

 posed to the lower rank of the palatines. In the mammals 

 a similar reversal of the sides of the molar teeth may be 

 noticed in comparing the upper and lower jaws. 



This sub-order does not embrace all the fish thatwant ven- 

 tral fins, there being many examples of such in other groups, 

 but it may be vie\ved as presenting an analogy to the Ceta- 

 cei among mammals. Neither does the vermiform type be- 

 long exchisively to these Apodals ; we shall find it mani- 

 fested repeatedly in other parts of the series of fishes. 



The table in small type gives the technical characters 



