PLATE XVI. Fig. 2. Nat. size.
Fig. 2. _b._ Twice nat. size.
Fig. 2. _a._ Magnified scale.
_A. gracillima; corporis altitudine partem vix nonam, capite sextam,
longitudinis æquante: oculis mediocribus: maxillis æqualibas, valde
protractilibus; commissurâ primum horizontali, posterius deflexâ:
dentibus velutinis, in maxillâ inferiore minutissimis: dorsali primâ
omnino pone ventrales reclinatas locatâ: squamis mediocribus, seriebus
longitudinalibus duodecim ad maximum dispositis, marginibus liberis
inciso-crenatis; vittâ laterali nitidè argenteâ._
D. 5—1/8; A. 1/17; C. 17; P. 12; V. 1/5.
D. 5—1/9; A. 1/19; &c.—
D. 6—1/10; A. 1/19; &c.—
LONG. unc. 2. lin. 6.
FORM.—Still more slender and elongated than the last species. Greatest
depth scarcely one-ninth of the entire length: head one-sixth.
Dorsal and ventral lines very little curved. General characters of
the head, snout and mouth, as in the _A. microlepidota_, but the
jaws more protractile. A row of minute velutine teeth in each jaw
most developed above. Eyes moderately large; their diameter nearly
one-third the length of the head; the space between them just equal
to their diameter. Opercle with the posterior margin nearly
vertical. Scales larger than in the _A. microlepidota_; the number
of longitudinal rows not exceeding twelve: their form different, and
rather peculiar, the anterior or free edge of each scale in some
instances presenting two or three processes, separated by deep
incisions; in others being irregularly notched or jagged, according
to the spot whence taken: the surface is marked with concentric
lines, but there is no fan of striæ on the basal half: the breadth
of the scale a little exceeds its length, and the basal margin is
irregularly sinuous.
First dorsal answering to the space between the tips of the reclined
ventrals and the anal. Length of the second dorsal exceeding the
intermediate space between it and the first. From the end of the
second dorsal to the caudal is rather more than one-fifth of the
entire length. Depth of the caudal fork not exceeding one-third
the length of the fin. The anal commences in an exact line with
the termination of the first dorsal: rather less than its
posterior half answers to the second dorsal. Pectorals rather
long, measuring nearly one-sixth of the entire length. Breadth of
the silver band one-fourth the depth of the body.
COLOUR.—“Body semitransparent, colourless; with a bright silver band
on each side; also marked with silvery about the head.”—D. The band
is remarkably bright, and well-defined, much more so than in the
last species.
I have ventured to consider this as a new species, though none of the
specimens in the collection, amounting to three in number, exceed two
inches and a half in length, and are probably not full-sized. The form
of the scales is so peculiar, that if it were only the young of some
described species, it could hardly fail to be identified by such a
character, which is not likely to be affected by age, nor to have
escaped the notice of an observer. Yet I can find none answering to it
in the “Histoire des Poissons.” The silvery band also is remarkably
bright; though the slenderness of the body, another of its
peculiarities, is perhaps due to immaturity. The fin-ray formula is
somewhat different in the three specimens, as shown above, but in other
respects they are similar.
Mr. Darwin’s notes state that this species was taken in the month of
September, in 39° S. Lat., 61° W. Long., several miles from the land.
This last circumstance, indeed, would seem to indicate that the
specimens were not so very young, as the fry of most fish keep close in
shore.