FISHES OF GREAT BRITAIN AND IRELAND. 



Class. PISCES. 



Vertebrate animals which, as a rule, are exclusively adapted for an aquatic 

 life, and have their extremities modified into fins. Respiring, almost invariably, 

 solely by means of gills :* possessing a heart with only two cavities, and being 

 cold-blooded. They are scaleless, partially, or wholly scaled, the scales being 

 sometimes in the form of osseous plates. 



Sub-class I. TELEOSTEI. 



Skeleton osseous. Brain distinct. Skull possessing cranial bones. Vertebrae 

 completely separated, and the posterior extremity of the vertebral column 

 bony, or having bony plates. Branckia3 free, and the water discharged through 

 a single aperture, protected by a bony gill -cover, or opercle : branchiostegal 

 rays present. A non-contractile bulbus arteriosus, having a pair of valves at 

 its commencement. Optic nerves decussating. Intestines without any spiral valve. 



Order I. ACANTHOPTERYGII. 



A portion of the dorsal, anal, and ventral fins unarticulated, forming spines.f 

 Air-bladder, when present, completely closed, not possessing a pneumatic duct. 



Geographical distribution. The spiny-rayed or Acanthopterygian order of fishes 

 appear to be most numerous in the ocean, preying upon their weaker neighbours. 

 Whereas, if we examine inland fresh waters, we observe the Malacopterygii as 

 the Salmonidce and Gyprinidce usurping their place ; these latter having solely 

 articulated, but no spinous, rays. 



First group Perciformes. 



Body elevated or oblong not elevated. No superbranchial organ. Spinous 

 dorsal fin well developed : anal similar to soft dorsal ; ventrals thoracic, usually 

 1/4 or 1/5. Vent remote from caudal fin and posterior to the ventral. 



Family, I PERCID^E. 



Percoidei, pt., Scicenoidei, pt., et Mcenides, pt., Cuv. ; Percidce, pt., Theraponidce, 

 pt., Hcemidonidce, pt., Richardson ; Percidce, pt., et Pristipomatidce, pt., G-unther ; 

 Ambassoidei, pt., Bleeker. 



Branchiostegals from five to seven : pseudobranchisB present. Form of body 

 generally oblong. Muciferous system of head rudimentary or but slightly 

 developed. Eyes lateral. No superbranchial organ. Preopercle entire or 

 serrated : cheeks not cuirassed. Mouth in front of snout, having a lateral cleft, 

 occasionally on the lower side, moderately or rarely very protractile. Teeth 

 in the jaws villiform, with or without canines, present or absent on the 



* Certain fishes, mostly residents within or near the tropics, as the Labyrinthici and Ophiocepha- 

 lidce, even when a bandage is fastened round their gill-covers, entirely precluding their 

 employment for respiratory purposes, are still able to live in water, provided they can obtain direct 

 access to atmospheric air. In the majority of fishes such a proceeding would be rapidly fatal. 



f There are some genera in which the fins can hardly be said to have any true spines, as among 

 the Trachinidce, Aulostomatidcc, Ophiocephalidui, $c. 



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