_T. corpore ovali, valde compresso, altitudine tertiam partem,
longitudinis, hâc ad basin furcæ caudalis mensá, æquante: osse
maxillari margine posteriore recto: pinnâ dorsali suprà, ventrales
accuratè exorienti; anali lævi, altitudine retrò cito decrescente;
radiis plicis membranaceis nullis: squamis in lineâ laterali 40, in
lineâ inter pinnas ventrales et dorsalem transversâ 14._
D. 1/10; A. 3/22, &c.
LONG. unc. 2. lin. 2.
FORM.—Depth and general form similar to those of the _T. rutilus_;
also the same number of rows of scales, the lateral line occupying
the eighth from the top. Anal smooth, and similar to that of the _T.
rutilus_ in form, but in the number of the spines and soft rays
agreeing with the _T. scabripinnis_. The maxillary straight, but
hardly so much dilated as in the last-named species, being of nearly
equal breadth throughout. The teeth are more numerous than in
either, amounting in the lower jaw to fourteen or more. The ventrals
are in an exact line with the commencement of the dorsal.
COLOUR.—Much as in the _T. scabripinnis_. The same silver band, only
more brilliant; also the same humeral spot, and the spot at the base
of the caudal extending along the middle rays.
Habitat, Rio de Janeiro.
The above description is that of two small specimens, similar to each
other, obtained by Mr. Darwin in a running brook at Socego, in the
province of Rio de Janeiro. They are probably not full grown; but so
evidently distinct from either of the last two species, the characters
of which are in some measure combined in them, that I have not hesitated
to give them a separate place. The silver band is more or less obvious
in all the species of this genus brought home by Mr. Darwin, but it is
much brighter in this than in any of the others.
5. TETRAGONOPTERUS INTERRUPTUS. _Jen._
PLATE XXIII. fig. 4.
_T. corpore ovali, valde compresso: altitudine tertiam partem
longitudinis totius æquante: ore parvo; osse maxillari brevissimo,
dilatato, margine posteriore recto: dentibus minutis,
multicuspidatis: dorsali subtriangulari, pone ventrales exorienti;
anali (in uno sexu?) scabrâ, altitudine retrò subito decrescente;
his pinnis plicis membranaceis nullis: squamis in lineâ
longitudinali 35, in lineâ inter pinnas ventrales et dorsalem
transversâ 10: lineâ laterali interruptâ, haud finem pinnæ
pectoralis attingente._
D. 1/10; A. 2/18; C. 18, &c.; P. 11; V. 7.
LONG. unc. 2. lin. 8.
FORM.—Oval, and not very dissimilar in general form to the _T.
rutilus_, but rather more elevated above the shoulder. Depth exactly
one-third of the entire length: head one-fourth of the same, caudal
excluded. Profile not exactly straight, but very slightly hollowed
out at the crown, then as slightly protuberant above the eyes,
whence it falls more rapidly in front, giving the snout a short and
blunt appearance. Mouth much smaller than in any of the preceding
species, owing to the extreme shortness of the maxillary, which is
broad, with the anterior margin curving outwards, but the posterior
one straight. Teeth very small; the points on the cutting edges
numerous (five or six on each tooth) and nearly equal; apparently
only one row on the intermaxillary, and the same in the lower jaw;
none on the maxillary. Eyes and nostrils as in the other species,
but the anterior orifice of the latter larger. Subopercle much
larger, forming a greater portion of the gill-flap. Scales
relatively larger; only ten in the depth, and thirty-five in the
length. They have no deep striæ on the basal portion, and
consequently no fan; but they are very regularly marked with the
usual finer striæ concentrically arranged, except on the free
portion where they become indistinct.
The lateral line occupies the sixth row of scales from the top, but is
very soon interrupted, coming to an end before it has reached the
length of the pectoral, and not carried over more than eight or nine
scales in the length. Dorsal subtriangular, commencing exactly at
the middle of the length, caudal excluded. Anal shorter than in the
other species, and not reaching so near the caudal; two spines, but
the first extremely minute. Caudal forked for half its length, the
lobes equal. Ventrals more forward than in the other species,
decidedly in advance of the dorsal, and attached at one-third of the
entire length; their axillary scale very small. Pectorals narrow,
reaching beyond them. No long folds of skin accompanying the rays of
the vertical fins.
COLOUR.—Not noticed in the recent state, in which, judging from its
appearance in spirit, it was probably silvery, or perhaps golden,
with somewhat of an olivaceous hue becoming deeper on the back.
There are evident remains of a bright longitudinal lateral band:
also of a black spot at the base of the caudal. The dorsal and the
anterior portion of the anal incline to dusky: the pectorals and
ventrals are slightly dusky at their extremities; there is also a
large irregular dusky stain on the back and shoulders anterior to
the dorsal fin.
A _second specimen_ differs from the above in being a trifle smaller,
and not quite so deep in the body. The anal is also decidedly
scabrous, as in the _T. scabripinnis_, and has one ray less in it.
The colours are similar, excepting that the fins are rather less
dusky, and the large dusky stain on the back and shoulders is
wanting.
Habitat, Maldonado.
This species is one of several that were taken by Mr. Darwin at
Maldonado, in the lake that had been suddenly drained, before alluded
to. It is immediately distinguished from all the others in this genus
above described, by its small mouth and abbreviated lateral line. The
circumstance of the anal fin being scabrous in only one of the specimens
leads to the suspicion that this may be a sexual character, perhaps
common to this and several species; and, judging from its somewhat less
depth, I conceive the specimen so distinguished in this instance to be a
male.