OlIDEliS OF FISHES. 243 



Each of these Ijraucliial cliambers opens externally by a single aper- 

 ture, the " gill-slit," which i« protected by a chain of bones, forming 

 the "gill-cover,'' and by a membrane supported by bony rays. In- 

 ternally the branchial chambers communicate with the throat by a 

 series of clefts or fissures, and the water required in respiration is 

 taken in at the mouth by a process analogous to swallowing. 



7. The nasal sacs never communicate behind with the throat 

 (pharynx). 



Tabular View or the Main Divisions of the Teleostei. 



Sob-order I. irALACOPiERi. — U.siially a complete series of iins, supported 

 by rays, all of whicli are soft^ or many-jointed (with tlie occasional exception 

 of the first rays in the dorsal and pectoral fins). A swim-bladder is always 

 present, and is always connected with the gullet by a duct. The skin is rarely 

 naked, and is mostly furnished with cycloid scales, hut sometimes ganoid scales 

 are present. 



Amongst the more important families iu tliis suh-nriler are the Eels [MvT'y- 

 nidrji), Herrings (Clupeido!), Pikes [Esocidu), Carp {t'l/j/rinidaj, Salmon and 

 Trout {Salinonidit), and Slieat-fishes [Siluridi/'). 



SUB-OBDEK II. Anacanthinf.— Fins entirely supported liy soft rays, and 

 never by spinous rays. Ventral fins either wanting or placed under tlie throat, 

 beneath or in ailvance of the pectorals. 



Tlie two leading families in this sub-order are the Cod, Ling, and Haihlock 

 family (Gadidce), and the Flat-fishes {Pleujvnectidce), comprising the Sole, 

 Turbot, Flounder, and others. 



ScB-oiiDEE III. Acanthoptebi. — Fius With oue or more of the first rays in 

 the form of undivided, infiexil:»le, spinoirs rays. Scales mostly ctenoid. Swim- 

 bladder without a duct. 



The leading families in this order are the Wrasses {Cijchdahrido:), the Perches 

 [Percidos), the Mackerels {Sciriiiheridce}, the Mullets [Micgllula ,) and the Gobies 

 [Oobiidce). 



Sub-order IV. Plectognatht. — Certain of the liones of the mouth (tlie 

 maxillary and pjra^inaxillary bones) immovably connected on each side of the 

 jaw. Integumentary skeleton in the form of ganoid plates, scales, or spines. 



The cliief families in this sub-order are the File-fishes {Balisiidie), and the 

 Trunk-fishes ( Ostraciontidce). 



Sob-order V. Lophobranchil— Gill arranged in little tufts on tlje bran- 

 chial arches. Integumentary skeleton in the form of ganoid scales. 



The two families contained in this division are the Sea-horses [Ilipjjocum- 

 pidfe), and tlie Pipe fishes (Suriynathida-). 



r);iDER IV. C4AN0IDEr. 



The fourth order of fishes is that of the Gnnoidi:!, including few 

 living forms, but having a great and varied development in jjast 

 geological epochs. The Ganoids are distinguished by the generally 

 imperfect develoiiment of the .skeleton, which i.s mostly cartilaginous 



