Dules malo, _Val.?_ Hist. des Poiss. tom. vii. p. 360.
_D. pinnis caudali, anali, dorsalique molli, nigro-marginatis; dorsali
profundè emarginatá, spiná ultimá radiis articulatis breviore;
operculo mucronibus duobus, inferiore maximo, armato; preoperculo
margine adscendenti levissimè denticulato, basali denticulis
fortioribus._
B. 6; D. 10/11; A. 3/12; C. 16, &c.; P. 13; V. 1/5.
LONG. unc. 4. lin. 5.
FORM.—General form resembling that of a small _Dace_. Greatest depth
about one-third of the entire length, caudal excluded. Length of the
head rather less. Dorsal line falling with the profile in one
continuous gentle curve. Eyes large; their diameter contained two
and a half times in the length of the head: the distance between
them less than one diameter. Suborbitals finely but very
conspicuously denticulated. Jaws nearly equal; the lower one a
little the longest. In each, a band of velutine teeth, with the
outer row rather longer than the others. Opercle with two points,
the lower one most developed. Preopercle with the limb striated: the
ascending margin with the denticulations so fine as to be hardly
sensible to the naked eye; those on the basal margin larger and more
obvious. Scales of a moderate size; about forty-three in a
longitudinal row; their free portions finely striated. Cheeks and
opercle scaly; crown naked, with a shallow groove above each eye.
Lateral line at first slightly descending, but afterwards straight;
its course, until past the dorsal and anal fins, a little above the
middle of the depth. Dorsal deeply notched: the anterior portion
consisting of nine spines; the first very short, and scarcely more
than half the length of the second; third and fourth longer,
increasing gradually; fifth and sixth equal and longest, equalling
half the depth of the body; seventh, eighth, and ninth, shorter, and
gradually decreasing; the tenth spine, with which the second portion
of the fin commences, is of the same length as the fifth, but not
quite so long as the soft rays which follow; these soft rays,
however, gradually become shorter, the last two not more than
equalling the second spinous. The whole space occupied by the dorsal
is more than one-third of the entire length. Anal commencing in a
line with the ninth dorsal spine; its own three spines gradually
increasing in length, but the second the strongest; soft portion of
this fin longer than the corresponding portion of the dorsal, and
terminating a little nearer the caudal. Vent in a line with the
seventh dorsal spine. Pectorals small, reaching to the vent.
Ventrals attached a little further back, and reaching a very little
beyond it. Caudal forked.
COLOUR.—(_In spirits._) Silvery, tinged on the back, and above the
lateral line, with bluish grey, and somewhat mottled in places with
darker spots. Fins yellowish grey, tinged with dusky. The caudal,
anal, and soft portion of the dorsal, are a little mottled with
dusky, besides having a black edging; there is also a conspicuous
black spot at the anterior angle of this last fin.
A second specimen is only three inches and a quarter in length; but
differs in no respect from the above, except in having one soft ray less
in the anal fin.
Habitat, River Matavai, Tahiti.
Several of the species in this genus are extremely similar as well in
form as in colours. Possibly that which I have here characterized as new
may not be distinct from the _D. malo_ of Valenciennes, which comes from
the same country; but the description in the “Histoire des Poissons” is
so brief, that it is hardly possible to determine this point with
certainty. It has, however, two, and one specimen three, soft rays less
in the anal fin. It is also closely allied to the _D. marginatus_, from
which it hardly differs, excepting in having the denticulations of the
preopercle rather stronger, and the tenth dorsal spine shorter in
relation to the soft rays which follow. The _D. marginatus_, however,
comes from Java. The species here described was found by Mr. Darwin in
Tahiti, in the river of Matavai.