Seriola bipinnulata, _Quoy et Gaim._ Voyage de l’Uranie (Zool.) p. 363,
pl. 61. f. 3.
—— —— _Cuv._ Regne An. (2d Edit.) tom. ii. p. 206.
FORM.—Elongated, and fusiform. Greatest depth contained four times and
a half in the length, measuring this last to the base of the caudal
fork. Head four times and a quarter in the same: depth of the head
not quite once and three quarters in its own length; the cheeks
nearly vertical. Snout pointed: profile straight, and but slightly
falling. Lower jaw a little longer than the upper, the commissure
reaching to beneath the orifices of the nostrils: maxillary very
conspicuous, and greatly dilated at its posterior extremity. A band
of minute velutine teeth in each jaw, broadest in front; a disk of
similar teeth on the vomer, and a band on each palatine. Eyes large;
their diameter one-fifth the length of the head; situated a little
above the middle of the cheek, and a little nearer the end of the
snout than the posterior margin of the opercle; exactly two
diameters between the eye and the end of the lower jaw. The nostrils
consist of two small, round, closely approximating orifices, the
anterior one partially covered by a membrane; situated rather nearer
the eye than the extremity of the snout. Preopercle with the
ascending margin vertical, and the angle at bottom rounded; the limb
very broad, and marked with veins, and between the veins, along the
basal margin, with fine striæ. The rest of the pieces of the
gill-cover, taken together, present a rounded and regularly curved
outline posteriorly; the line of separation between the opercle and
subopercle ascends obliquely backwards from a point about two-thirds
down the posterior margin of the preopercle; that between the
subopercle and the interopercle (which last is well developed)
passes downwards and backwards, forming an angle of about 45° with
the axis of the body. Branchial aperture large; the membrane deeply
cleft. Snout, jaws, and pieces of the opercle, smooth and naked;
cheeks scaly, the scales on the upper part of the cheek, between the
eye and the upper angle of the preopercle, being of a narrow pointed
form. The scales on the body are of a moderate size, oval, marked
with fine concentric circular striæ, with a fan of coarser diverging
striæ on their concealed portion. The lateral line is smooth
throughout its length, and runs nearly straight from the upper angle
of the opercle to the caudal, its course being a little above the
middle.
The first dorsal commences at about one-third of the entire length,
measuring this last as before: it is low and inconspicuous,
consisting of only six weak spines, of which the third and fourth
are somewhat the longest, but whose length is less than one-fifth
of the depth of the body. The length of the fin itself is rather
less than half the depth. Second dorsal closely following, and
much longer; of the form usual in this family, with the anterior
portion elevated and somewhat triangular, but beyond the ninth ray
low and even: its spine half the length of the first soft ray: its
greatest elevation contained about two and a half times in the
depth. The last two rays of this fin are broke away from the rest,
with an intervening space, to form a spurious finlet, and are
rather longer, the last especially, than those which precede. The
anal commences opposite the fourteenth ray of the second dorsal,
and is similar in form to that fin, but of course shorter, and
also less elevated at its anterior extremity: finlet and the
intervening space exactly corresponding. Caudal deeply forked; the
lobes very long and pointed, each equalling nearly one-fourth of
the entire length; the middle rays not one-fourth the length of
the lateral ones. Pectorals attached a little below the middle; in
length a little exceeding half that of the head. Ventrals about
the same size as the pectorals, but attached a little further
back. A slight elevation at the sides of the tail, but no distinct
keel, properly so called.
D. 6—1/24—I; A. 1/16—I; C. 17, &c.; P. 20; V. 1/5.
Length 18 inc. 3 lines.
COLOUR.—“Band on the side azure blue; above a duller greenish blue;
beneath two greenish metallic stripes: lower half of the body snow
white.”—D. No trace of the longitudinal stripes remains in the dried
skin.
Habitat, Keeling Island, Indian Ocean.
A tolerably exact figure of this species occurs in the Zoological Atlas
of Freycinet’s Voyage, but I can find no notice of it in the “Histoire
des Poissons” of Cuvier and Valenciennes. Although referred by Cuvier in
his “Regne Animal” to _Seriola_, it rather departs from that genus in
some of its characters. Independently of the spurious finlets in the
dorsal and anal fins, which separate it from all the other species, I
see no trace of any reclined spine before the first dorsal, nor of two
free spines before the anal; in both which respects _Seriola_ is said to
resemble _Lichia_. Possibly, however, as Mr. Darwin’s specimen is a
dried skin, these characters may have been destroyed in the process of
preparation. And to the same cause, perhaps, is to be attributed the
circumstance of my not being able to observe more than one spine in the
true anal, Quoy and Gaimard mentioning two. On the other hand, these
naturalists appear to have overlooked the narrow pointed scales on the
upper part of the cheeks, which are of a different character from the
scales on the body.
Mr. Darwin’s specimen of this species was obtained at the Keeling
Islands. The one figured in Freycinet’s Voyage was procured at Papua or
New Guinea. It probably, therefore, has a considerable range over the
Indian Ocean.