_P. nigricanti-fusco undique punctata; vertice, fronte, rostro usque
ad nares, et infraorbitalium parte posteriori, squamatis; squamis,
in capite ciliatis scabris, in corpore sublævibus._
B. 7; D. 9—1/11; A. 3/9; C. 17; P. 15; V. 1/5.
LONG. unc. 11; lin. 5.
FORM.—Much more elongated than the _common Perch_, with the back less
elevated. Depth, beneath the commencement of the first dorsal, not
quite equalling one-fifth of the entire length. Thickness, in the
region of the pectorals, about two-thirds of the depth. Head not
quite one-fourth of the entire length. Profile falling gently from
the nape in nearly a straight line at an angle of about 45°: at the
nape the dorsal line rises so as to interrupt its continuity with
the slope of the profile, but it is nearly horizontal along the base
of the dorsal fins. The jaws are nearly equal, but when the mouth is
closed, the upper one appears somewhat the longer. A band of
velutine teeth in each jaw, as well as on the vomer and palatines.
Maxillaries when at rest nearly concealed beneath the suborbital
bones: these last with their lower margin distinctly denticulated;
their surface presenting several small hollows. Eyes rather above
the middle of the cheeks, and about equidistant from the extremity
of the snout and the posterior margin of the preopercle; their
diameter is one-sixth of the length of the head; the distance from
one to the other equals one diameter and a half. Nostrils double, a
little in advance of the eyes; the first orifice oval, the second
round. Preopercle rectangular, with the angle rounded; the ascending
margin finely denticulated, the teeth almost disappearing at the
top; towards the angle the teeth become stronger and point
downwards; they are also stronger and more scattered along the basal
margin, inclining here a little forwards. Opercle with two flat
sharp points, one a little below the upper angle, the other about
the middle and terminating the gill-cover. Both the subopercle and
interopercle have their margins obscurely denticulated: the margin
of the former is rather sinuous, and passes obliquely forwards and
downwards to form a continuous curve with that of the latter. Crown,
forehead, upper part of the snout as far as the connecting line of
the nostrils, posterior half of the suborbitals, cheeks, and all the
pieces of the gill-cover, excepting the lower limb of the
preopercle, covered with small scales, which are in most instances
ciliated with a varying number of denticles, and feel rough to the
touch: the extremity of the snout, anterior portion of the
suborbitals, maxillaries, and lower jaw are naked. Above each orbit
is a small semicircular granulated plate, with the granulations
disposed in striæ. The suprascapulars terminate in an obtuse
projecting point. The humeral bone forms a large osseous triangular
plate above the pectorals, the salient angle terminating in three
small teeth. Course of the lateral line a little above one-third of
the depth till it arrives beneath the second dorsal, where it bends
down to half the depth. Scales on the body larger than those on the
head, of an oblong form, rounded at their free edges, which are
scarcely at all ciliated, and for the most part quite smooth to the
touch; their concealed portion not wider than the free, with a fan
of fourteen striæ; the rest of their surface more finely striated.
The first dorsal commences a little beyond a vertical line from the
termination of the humeral plate, and is almost continuous with the
second, being only separated by a deep notch; the space occupied by
the two dorsals together is exactly one-third of the entire length:
spines strong; the first scarcely more than one-third the length of
the second, which is very little shorter than the third; this last
longest, equalling rather more than half the depth; rest of the
spines gradually decreasing to the last, which is of the same length
as the first. The second dorsal commences with a slender spine, not
half the length of the first soft ray, which last is simple, the
others being branched; third and fourth soft rays longest; the
succeeding ones slowly decreasing to the last, which is rather more
than half the longest. Anal preceded by three spines, the first of
which is very short; second much longer and very stout; third of
about the same length as the second, but much slenderer; the first
and second separated by a wide membrane from the third, which is
closely united to the first soft ray; these last longer than those
of the second dorsal, but in other respects similar. The anal and
second dorsal terminate in the same vertical line; and the last ray
is double in both fins. Between them and the caudal is a space
equalling one-fifth of the entire length. The caudal is slightly
notched. The pectorals are rather pointed, their length equalling
two-thirds that of the head. Ventrals immediately beneath them, and
of about the same length; the first soft ray longest, and more than
twice the length of the spine which precedes it.
COLOUR.—In spirits this fish appears yellowish brown, deepening on the
back but becoming paler on the belly, and covered all over with
small dusky spots, one occupying the base of each scale.
Habitat, Santa Cruz River, Patagonia.
[Illustration:
_Fish Pl. 2._
_Drawn from Nature on stone by Waterhouse Hawkins._
_Serranus albo-maculatus, ½ Nat. Size._
]
No true perch had been obtained from South America until M. D’Orbigny
discovered one in the Rio-Negro, in North Patagonia, which has been
since described by Valenciennes, under the name of _P. trucha_.[1] The
present species was found dead by Mr. Darwin, high up the river of Santa
Cruz, in South Patagonia. It is evidently very closely allied to the _P.
trucha_, and is spotted in a similar manner; but it appears to differ in
the scales not advancing on the snout beyond the nostrils, or covering
more than the posterior half of the suborbitals. Those on the body are
also particularly characterized by being so smooth, as hardly to
communicate any sensation of roughness when the hand is passed from the
tail towards the head, though the head itself is rough. This
circumstance has suggested the specific name. This species further
disagrees with the one above alluded to in having the caudal slightly
forked, not rounded; and in having two soft rays less in the second
dorsal, and one less in the anal. Valenciennes’s description, however,
of the _P. trucha_ is very brief; on which account I have been the more
minute in that of the _P. lævis_.
This perch, with _P. trucha_, would almost seem to form a subordinate
division in the genus, distinguished from that embracing all the other
described species, by the character of the scales covering a large
portion of the head which gives it a remarkable sciænoid appearance.
Both species may be known from all the North American perches, by their
having the body spotted instead of banded, and by the smaller number of
rays in the first dorsal. In this last character they agree with the _P.
ciliata_, and _P. marginata_ of Cuvier and Valenciennes.