OEDEKS OF FISHES. 243 



Each of these branchial chambers opens externally by a single aper- 

 ture, the " gill-slit," which is 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 reqviired 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 op the Main Divisions op the Teleostei. 



SuB-OKDER I. Malaoopteri. — Usually a complete series of fins, supported 

 "by rays, all of which are soft, or many-jointed (with the occasional exception 

 of the iirst 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, but sometimes ganoid scales 

 ai'e present. 



Amongst the more important families in this sub-order are the Eels (Murce- 

 nidce), Herrings (Clupeidee), Pikes {Esocidce), Carp (Cyprinidce), Salmon and 

 Trout (Salmonidce), and Sheat-fishes (Siluridce). 



Sub-order II. Anaoanthini. — Fins entirely supported by soft rays, and 

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

 beneath or in advance of the pectorals. 



The two leading families in this sub-order are the Cod, Ling, and Haddock 

 family [Oadidce), and the Flat-fishes [Pleuroneclida), comprising the Sole, 

 Turbot, Flounder, and others. j 



Sdb-ordeb III. Aoanthopteri. — Fins with one or more of the first rays in 

 the form of undivided, inflexible, spinous rays. Scales mostly ctenoid. Swim- 

 bladder without a duct. 



The leading families in tliis order are the Wrasses {Cyclolabrida'), the Perches 

 (Percidce), the Mackerels [Saomheridie), the Mullets (Mugilida;,) and the Gobies 

 (Gobiidce). 



Sub-ordeb IV. Plectognathi.— Certain of the bones of the mouth (the, 

 maxillary and prajmaxillary bones) immovably connected on each side of tl 

 jaw. Integumentary skeleton in the form of ganoid plates, scales, or spine-s. 



The chief families in this sub-order are the File-flshes (Balistidw), and the 

 Trunk-fishes (Osiracionlidw). 



Sub-order V. Lophobranohii. — Gill arranged in little tufts on the bran- 

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



The two families contained in this division are the Sea-horses (liipxiooam- 

 pidcc), and the Pipe-fishes (Syngnalhidai). 



Order IV. Ganoidei. 



The fourth order of fishes is that of the Ganoidei, including few 

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

 geological epochs. The Ganoids are distinguished by the generally 

 imperfect development of the skeleton, which is mostly cartilaginous 



