xxii INTRODUCTION. 



The great class of Blshes (Pisces,) is by some naturalists divided into the following 

 six sub-classes, (i) Tdcostci, (2) Dipnoi, (3) Ganoidei, (4) Chondropterygii, (5) Cyclostomata , 

 (6) Leptocardii. I follow Dr. Glinther in the following classification : — 



The first sub-class of TELEOSTEI contains all those fishes which have a complete bony 

 skeleton ; this sub-class comprehends more species than all the other sub-classes put together, 

 and nearly all our British fresh-water species belong to this great sub-class. It contains the 

 following orders, which are again themselves divided into different families, the families into 

 genera, and the genera into species. 



Order I. — Acanthopterygii, from aKavBo<i, "a spine," and Trrepv^, "a wing," or "fin," 

 contains those fishes whose fin rays form spines, as in the Common Perch. The air-bladder, 

 when present, has no pneumatic duct. 



Order II. — Acanthopterygii-Pharyngognathi, contains those species in which the in- 

 ferior pharyngeal bones coalesce, as in the marine Labrida or Wrasses ; air-bladder without 

 pneumatic duct. There is no British fresh-water species belonging to this order. 



Order III. — Anacanthini, in which, excepting in one genus, the vertical and ventral 

 fins are without spinous rays; from a, "not,"' and aKav6o<;, "a spine." Air-bladder, when 

 present, without pneumatic duct. This order contains two sub-orders, {a) Gadoidei (Codfish 

 families), and {b) Pleuronectoidei (Flat-fish, Soles, Turbots, etc.) We have a single fresh- 

 water representative of sub-order {a) in the Eel-pout, or Burbot, (Lota vulgaris J : and of 

 sub-order {b) in the Flounder (Picuvonectcs JJesusJ, which is known to ascend our rivers to a 

 considerable distance ; some years ago Flounders were common in the Severn as high up as 

 Shrewsbury. 



Order IV. — Physostomi. This is an extensive order, and comprises several families, as 

 the Cyprinida, ClupcidcB, Esocidcc, Salmonidcc, and Murcenida;, all of which have British fresh- 

 water representatives. The fin rays are articulated ; the first of the dorsal and pectoral being 

 sometimes more or less bony; the spineless ventral fins, when present, are not situated near 

 the pectorals, but on the abdomen. The^Nord. PIiysosh?!ii is from the Greek <^vaa, "a bladder," 

 and arofj-a, "a mouth," in allusion to the air-bladder, when present, being connected with 

 the mouth or gullet by means of the pneumatic duct, which is the invariable accompaniment 

 of the air-bladder in this order. Carp, Shad, Pike, Salmon, and Eel are fresh-water repre- 

 sentatives of this order. • 



Order V. — Lophobranchii, from Xocjio'^, "a tuft," and (Bpajxia, "the gills." In this order 

 the gills are formed of small rounded lobes, and are not laminated. The air-bladder has 

 no pneumatic duct. Marine examples are Sea-horses (Hippocampus), and Pipe-fishes [Syngnai/iiis). 

 There is no fresh-water representative. 



Order VI. — Plectognathi, from -n-Xe^To?, "twisted," or "fastened together," and yvado';, 

 "the jaw," because generally the maxillary and praemaxillary bones of the mouth are 

 immovably connected on each side of the mouth, as in the genera Ostracion (Trunkfish), 

 Balistes (Filefish), and Orthagoriscus (Sunfish). Of this order there is no British fresh-water 

 representative ; indeed Giinther tells us that nearly all are marine fishes. The air-bladder 

 has no pneumatic duct. 



Sub-class II. — DIPNOI is one of the most interesting of all the sub-classes ; the word 

 means "double breathers." This has already been explained on pages xix-xx, to which the 

 reader is referred. Two genera and two species only are known, the Protopterus anticctcus of 

 tropical Africa, which has three external branchial appendages, and the Lepidosircn paradoxa of 

 Brazil, which is destitute of external appendages. 



