IV.—_THE FISHES OF THE IRISH SEA. 
In this section the fishes are arranged systematically in Zoological Classifi- 
eation,* beginning with what are usually regarded as the highest or most 
specialized forms. 
Class P'SCES! 
Vertebrate aquatic animals with an anterior and a posterior pair of 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.-— TELEOSTED 
Skeleton bony, vertebra solid. Heart with a bulbus, and no conus 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 PHYSOCE YS 
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 Salmonide. 
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, 
