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 tins 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 ( Trichiuridce) scarcely possess¬ 
ing what can be denominated true spines, while these are also wanting in the 
family ( Scombresocidce) 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 Percidee. 
The first representatives of the spine-finned fishes are the perches, which, with 
several allied families, belong to a sectional group ( Perciformes ) 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 vertebras; 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 vertebrae 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 brandies 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 has 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 fins, 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 ( Perea fluviatilis), which is a fish of wide 
True Perches ^ .. . , ... 
distribution, and one too familiar to require detailed description, is 
the type of a small genus, agreeing with eight others in the following characteristics. 
3 They are said to be thoracic when in the same vertical line as the pectoral fins, and jugular when in advance 
of them. 
