IV. THE FISHES OF THE IRISH SEA. 



In this section the fishes are arranged systematically in Zoological Classifi- 

 cation,* beginning" with what are usually reg-arded as the hig-hest or most 

 specialized forms. 



Class PISCES 



Vertebrate aquatic animals with an anterior and a posterior pair ot limbs in the 

 form of fins ; having median fins supported by skeletal or dermal fin-rays ; provided 

 with jaws, and having a pair of blind nasal sacs opening to the exterior but not into the 

 mouth ; breathing by gills only, which open by one or more gill clefts near the front of 

 the body ; heart entirely venous ; a series of modified scales and sensory organs form a 

 "lateral line" along the side of the body. 



Division I. TELEOSTOMI 



Branchial arches and gills covered by one large opercular fold ; gills free 

 upon the gill arches, not enclosed in pouches. Skeleton largely or wholly bony, with 

 both membrane and cartilage bones. Mouth terminal or nearly so. The pelvic fins 

 usually placed far forward on the body. The roof of the fore-brain is not nervous. The 

 ova are numerous and small. 



Order I. TELEOSTEI. 



Skeleton bony, vertebrae solid. Heart with a bulbus, and no conns arteriosus ; no 

 intestinal spiral valve. Tail homocercal. Optic nerves simply cross. There are seven 

 branchiostegal rays supporting a part of the gill cover. 



This includes our ordinary bony fishes, as distinct from the sturgeons (Chondrostei), 

 and the cartilaginous fishes (Elasmobranchii), such as skates and sharks. 



Section PHYSOCLYSTI. 



Air-bladder, when present, without a duct in the adult animal. Gills pectinate. 

 This includes the great bulk of our ordinary bony fishes, as distinct from the 

 Herring tribe and the Salmonidae. 



A. ACANTHOPTERI. 



The dorsal fin is protected by some unjointed spines. The position of the pelvic 

 fins is variable. The inferior pharyngeal bones are paired. 



This includes a very large number of our common shore fishes, most of which are 

 not marketable. They are distinguished by their stiff spiny fins from the important food- 

 fish of the Cod and flat-fish tribes (Anacanthini) which follow. 



* The classification given here takes no account of fossil forms, nor of groups unrepresented in our seas. 



