■ .’!■
■ 11:1
Ji-
Pacific Oceans. Mr. Darwin’s specimen agrees in every respect with the description
in the “ Histoire des Poissons,” except in having one ray more in the anal fin :
its length is not quite five inches.
2 . A c a n t h u r u s h u m e r a l is . C u v . et Val.
Acanthurus humeralis, Cuv. et Val. Hist, des Poiss. tom. 3 . p. 170.
F o r m .— General form oblong-oval. G reatest depth ju st behind the insertions of the pectorals;
contained exactly twice in the length of the oval of the body (measuring this last from the end
of the snout to the base of the caudal spine), and three times in the entire length (measuring
this last to the extremities of the lobes of the caudal fin.) Profile convex before the eyes,
whence it descends nearly vertically to the mouth. H eight of the head a little exceeding its
own length. Eyes very high in the cheeks, and in front of each a grooved line passing horizontally
forwards towards the nostrils; which last consist of two small round orifices, the
anterior one larger than the other, and partially covered by a membranous flap. There are
seventeen teeth in the upper jaw , and sixteen in the lower : those above have the cutting edges
crenated, and likewise the lateral edges for nearly h alf way down ; this most observable in the
middle ones, in which the crenations amount to eight or ten in num ber: those below similar,
but with the crenations not quite so numerous, and in some of the teeth at the sides of the jaw
almost confined to the cutting edges. Scales m inute ; those taken from the middle of the body
appear of an oblong form, their apical portions dotted, and ciliated with from twelve to eighteen
very minute denticles, their surface marked with extremely fine delicate striæ , not distinguishable
without a strong lens.
The lateral line follows the curvature of the back, a t about one-fifth of the depth. The spine
on the sides of the tail is strong, and sharp-pointed, and very slightly bent. No reclined spine
before the dorsal. Both the fin ju st mentioned and the anal have their soft portions terminating
posteriorly in rather an acute angle : also both have a scaly membrane a t the base, and rows
of minute scales between the soft rays extending for about oiie-third or more of their length.
The first ray of the anal is very minute, and so much concealed in the skin as to be easily
overlooked. The filaments of the caudal are sharp-pointed, and extend as far again as the
middle rays : the upper one rather longer than the other. The pectorals are contained three
times in the length of the oval of the body. V entrals attached a little further back, sharp-
pointed, and term inating in the same vertical line with the pectorals, both being laid back.
D. 9/23 ; A. 3/23 ; C. 16, &c. ; P. 16 ; V. 1/5.
Length, to the end of the caudal lobes, 7 inches.
C o l o u r .—The colours appear to have been exactly as described in the “ Histoire des Poissons.”
Mr. Darwin’s notes taken from the recent fish state, “ splendid verditer blue and green ;” but do
not enter into the details of the markings.
H abitat, Tahiti.
Obtained at Tahiti, where it had been previously found by MM. Lesson
and Garnot. Mr. Darwin’s specimen accords with the characters given by Cuvier
é
and Valenciennes, except in having two soft rays less in the dorsal, and one less
in the anal. Their description, however, is not very detailed.
F a m il y .— A T H E R IN ID ® ,
1. A t h e r in a a r g e n t in e n s is . C uv.et V al.t
Atlierina argentinensis, Cuv. et Val. Hist, des Poiss. tom. x. p. 350.
F o r m .— D epth exactly one-sixth of the length, measuring-this last to the end of the middle caudal
rays. The length of the head is five and a-half times in the same, measuring this last to the end
of the caudal lobes. Thickness of the body at least h alf the depth. Head broad and flat, its
breadth across the crown behind the eyes equalling three-fourths of its depth. Snout rounded
horizontally, but sharp vertically. The profile is perfectly horizontal; and one uniform straight
line extends from the extremity of the upper Jaw to the commencement of the second dorsal.
V entral line sw'elling a little outwards, with its greatest curvature about the middle. Upper
jaw a very little longer than the lower, which ascends to meet it a t an angle of 4 6°; gape not
reaching more than half-way to the eye, a t first horizontal, afterwards deflexed. In each jaw
two rows of teeth, stronger and more developed than usual in this genus, widely asunder, and
at irregular intervals: in the upper jaw these two rows are eq u al; in the lower the outer row
is stronger than the in n er: the outer row above contains about thirty-two or thirty-three
teeth ; that below twenty-six or tw enty-eight: no teeth on the tongue, and scarcely any that
can be seen on the vomer or palatines, though a slight roughness can be felt on the last two.
Eyes moderately la rg e ; tlieir diameter a very little less than one-fourth the length of the
head ; situate a little in advance of the middle point, and also a little above the middle of the
depth. Cheeks and gill-covers scaly. Form of the scales of the body, as well as the number
of longitudinal rows, exactly as stated by Cuvier and Valenciennes. The same may be said of
the lateral line, and the situation of the dorsal fins. The second dorsal and anal terminate in
the same vertical line. Pectorals exactly the length of the head. Ventrals attached immediately
below the tips of the pectorals. B readth of the silver band, which runs straight along
the middle of the sides, exactly one-fifth of the greatest depth of the body.
D. 5—1/9; A. 1/19; C. 17, & c.; P . 15; V. 1/5.
Length 8 inches.
C o l o u r .— “ Silvery, with a silver lateral b an d: above bluish grey.”— D . In spirits, it appears
greenish brown, becoming deeper above the silver band and on the ridge of the back : the free
margins of the scales are finely dotted with black : the rays of the caudal have been worn at
the tips, but there is a trace of the dusky edging noticed by C uvier: the pectorals are also
stained with dusky.
H abitat IMaldonado.
I conceive there is but little doubt of this being the A . Argentinensis of
Cuvier and V alenciennes; but as the description in the “ Histoire des Poissons”
is short, I have thought it advisable to give a more detailed one of the above