PERCH TRIBE. 335 



Physoclystous group are distinguished by the general absence of a duct to the 

 air-bladder (when present), by the parietal bones of the roof of the skull being 

 always separated from one another by the intervention of the supraoccipital, and 

 by the pelvic fins being in most cases either thoracic or jugular 1 in position. 

 Regarding, however, the spine-finned fishes as constituting a separate suborder, 

 they are distinguished, in addition to the foregoing characters, by some of the 

 anterior rays of the dorsal, anal, and pelvic fins usually taking the form of strong, 

 unjointed, bony spines. It must, however, be acknowledged that this character is 

 one of but little importance; some of the hair-tails (Trichiurida ) scarcely possess- 

 ing what can be denominated true spines, while these are also wanting in the 

 family (Scomln-esocidce) to which the flying-fishes belong. In all cases the gills 

 are comb-like, the pectoral arch is suspended from the skull, and interclavicles 

 are wanting. 



The Perch Tribe, — Family PercidsE. 



The first representatives of the spine-finned fishes are the perches, which, with 

 several allied families, belong to a sectional group {Perciformcs) of the suborder, 

 characterised by the lower pharyngeal bones being generally separate, and the 

 scales usually of the ctenoid type. The preopercular bone of the gill-cover has no 

 bony stay connecting it with the eye ; the spinous portion of the dorsal fin is well 

 developed : none of the additional rib-like bones known as epipleura are attached 

 to the bodies of the vertebrae ; the pelvic fins are thoracic in position, and have 

 usually five (rarely four) branched rays ; and the supporting bones (pterygials) of 

 the pectoral fins are longer than broad, and of a more or less distinctly hour-glass 

 form. The perch family, as restricted by Mr. Boulenger, is distinguished by the 

 following characters. In the skeleton the anterior vertebras have no transverse 

 processes, but in the dorsal part of the series all or most of the ribs are attached 

 to such processes. There are two nostrils on each side ; the gill-membranes are free 

 from the isthmus, or space between the two branches of the lower jaw and gill- 

 openings : there are four pairs of gills, with a slit behind the fourth ; the gill-rays, 

 or branchiostegals, vary from six to eight on each side; more or less fully- 

 developed false gills are generally present; the soft portion of the dorsal fin is not 

 very much more developed than the anal; and the latter lias either one or two 

 spines. In common with the two following families, the perches are further 

 characterised by the general presence of a lateral line, continuous from the head to 

 the tail, the usual absence of scales from the median tins, the simple conical teeth, 

 and the absence of barbels round the mouth. In form the body is more or less 

 elongate, compressed, and cylindrical, although rarely it may be slightly compressed. 

 As now restricted, the family includes a dozen genera inhabiting the fresh waters 

 of North America, Europe, and Western Asia: but the members of the genera 

 Lucioperca and Percarina enter salt water. All are carnivorous 



The common perch (Perca fluviatUis), which is a fish of vide 



True Perches. ,. , „ .,.' , . -, i , 



distribution, and one too familiar to require detailed description, is 

 the type of a small genus, agreeing with eight others in the following characteristics. 



1 They are said to be thoracic when in the same vertical line as the pectoral fins, and jugular when in advance 

 of them. 



