PLATE XXIV. Fig. 1.
_A. obscurè plumbeus; fasciis nigris transversis: maxillis æqualibus._
B. 3; D. 11; A. 2/14; C. 16, &c.; P. 18; V. 7.
LONG. unc. 9. lin. 6.
FORM.—General form somewhat resembling that of the _Mackarel_,
elongated, and approaching to fusiform. Greatest depth about the
middle, equalling one-sixth of the entire length. Line of the back
and profile nearly straight, the latter falling very little.
Greatest thickness rather more than half the depth. Head small,
contained about five and a half times in the entire length. Snout
short, but rather acute. Mouth with a moderate gape reaching to
beneath the anterior angle of the eye: when shut, both jaws equal,
the lower one ascending at an angle of 45° to meet the upper; when
open, the lower one a little the longest. Margin of the upper jaw
formed by the intermaxillary, the maxillary appearing behind it. A
single row of small but sharp teeth extending along the entire
margins of both jaws: a double row of similar teeth, but stronger
and more curved, down the middle of the tongue; also a double row
along the middle of the vomer. Eyes moderate; their diameter four
and a half times in the length of the head; distant about one
diameter and a quarter from the end of the snout, and with an
interval between them of about one and a half. Nostrils with two
orifices, both roundish, one before the other, with a little
interval between, the posterior one rather the largest. Two distinct
pores on each side of the crown, one behind the other with an
interval between, above and rather behind the eyes. Gill-opening
very large, the membrane with only three flattened rays, deeply
notched beneath, the notch reaching to beneath the middle of the
eyes. All the pieces of the opercle present, but the interopercle
only just appearing behind the angle of the preopercle, and the
subopercle forming but a narrow lanceolate lamina beneath the true
opercle, which last constitutes the greater portion of the
gill-flap, and is of an oblong form, the posterior margin being cut
straight and vertical.
The whole skin perfectly naked everywhere, without the least vestige
of scales. No lateral line, except a faint streak, passing along the
middle of the sides, be so called. Dorsal commencing at the middle
of the length, this last being measured to the base of the caudal
fork; of the same form as in the ordinary species of the genus
_Salmo_; its greatest height a little exceeding its length, which
last is rather more than half the depth of the body; first ray
simple, the rest branched. Adipose small, and just half-way between
the end of the dorsal and the base of the caudal. Anal of a somewhat
triangular form, the margin sloping very much off backwards,
commencing a little beyond the tip of the reclined dorsal, and
terminating opposite the adipose, or perhaps a trifle beyond it; two
small spines at its commencement; the first two soft rays simple,
the others branched. Caudal forked for half its length, the lobes
equal; the whole fin contained about six and a half times in the
entire length; the accessory rays very numerous, and partially
fringing the upper and lower edges of the tail. Pectorals attached
behind the gill-opening, rather below the middle, about two-thirds
the length of the head, of a somewhat triangular form, the rays
gradually shortening from the first, which is the only one
unbranched. Ventrals attached a very little in advance of the
dorsal, rounded, or almost cut square at the ends, the rays being
all nearly equal. They are scarcely shorter than the pectorals: the
space between their insertion and the commencement of the anal is
nearly double their own length. There is no long scale or appendage
of any kind in their axillæ.
COLOUR.—“Dull leaden colour.”—D.—In spirits it appears brown. The
sides are banded with some irregular transverse zebra-like marks,
not noticed by Mr. Darwin, reaching from the back down two-thirds or
three-fourths of the depth, some terminating sooner than others. All
the fins brownish.
Habitat, Falkland Islands.
Mr. Darwin obtained three specimens of this remarkable fish all
precisely similar, from a fresh-water lake in the Falkland Islands, in
March. The lake was not far from the sea, and connected with it by a
brook. He adds in his notes that the species is common there; that it is
good eating, and grows to be about half as large again as the
individuals procured.
One of these specimens was dissected by Mr. Yarrell and myself, and
presented the following internal characters, which are of importance to
be noted. The coats of the stomach were thick and muscular; the
œsophageal portion with prominent longitudinal plicæ. Its contents, so
far as they could be ascertained, consisted of the remains of
caddis-worms. The intestine was large, without any cœcal appendages, but
with one spiral convolution at the end of the first third of its length
from the pyloric orifice: the entire length of the canal was four
inches. The air-bladder was large, undivided, and of the same general
form as in many of the _Salmonidæ_. There were two elongated flattened
lobes of roe nearly ready for exclusion. The anal and sexual orifices
were separated, but enclosed in a tubular sheath, common to both,
directed backwards; the sheath itself lying in a groove in the abdomen,
and five-eighths of an inch in length: the opening to the cavity of the
abdomen and sexual organs was at the extreme end of this sheath, and
partly closed by two lateral valves; the opening to the intestine,
three-eighths of an inch short of the extremity.