'.I
I '« 'ì
considerably. Maxillary narrow, and of nearly equal breadth throughout, curving backwards.
Teeth with their cutting edges dentated, the middle point much the most developed, with one
or two smaller ones on each side : two rows of such teeth on the intermaxillary, and one in
the lower jaw, this last row with scarcely more than eight or ten teeth in it. No teeth on the
maxillary, vomer, palatines, or tongue. Eyes round, rather large, their diameter three and a
half times in the length of the head, distant not so much as one diameter from the end of the
snout. Nostrils with two orifices, the posterior one a narrow curved slit, the anterior one a
round hole. The suborhital forms a somewhat triangular naked disk beneath the eyes, with
radiating veins. Posterior margin of the opercle very little curved : subopercle narrow, and
small, forming but a small portion of the gill-flap.
About seventeen scales in the depth, and forty-six in the lateral line, which last bends
downwards rather below the middle, and is continued quite to the caudal. A scale taken from
the middle of the side below the lateral line is somewhat rounded anteriorly, the basal margin
being straight ; the surface marked with very fine numerous concentric striæ, and with two
coloured deeper striæ on the free portion diverging from the centre in a V-like form : some
scales have three or four of these coloured striæ, drawn more or less regularly.
Tho dorsal commences in about the middle of the entire length, excluding the caudal
and narrow part of the tail; of a triangular form, its greatest height equalling the depth to the
lateral line. Pectorals narrow, shorter than the head, attached below the bottom of the gill-
opening, and reaching rather beyond the insertion of the ventrals, which last are in a vertical
line with the commencement of the dorsal and shorter than the pectorals. Anal long, commencing
a very little beyond the tips of the reclined ventrals; the anterior portion rather more
than half the height of the dorsal, but the posterior much lower, sloping rapidly off; two spines,
the first very minute, the second about one-third the length of the first soft ray; the last soft ray
double. The anal terminates nearly in a hne with the adipose, which is small. Caudal forked
for half its length : the lobes equal. Many of the rays in the vertical fins, more especially the
dorsal and anal, are accompanied through nearly half their length from the bottom by membranous
folds of skin. There are also some small scales along the base of the anal, but
none apparent on tbe dorsal. In the axillæ of the ventrals is an elongated scale, not half
their length.
C o l o u r .—“ Back bluish silvery, with a silver band on the side: a bluish black spot behind the gills.
Fins pale orange ; tail with a black central band.”—D.—There is now not much trace of the
silver band, or the black band on the tail. The humeral spot is, however, still very distinct.
H abitat, the Rio Parana, South America.
This species was taken by Mr. Darwin in October in the Rio Parana, as high
up as Rozario. I cannot ascertain that it is described, though there is much resemblance
between it and the species figured in Seba.* It differs from the T.
chalceus of Spix, in its much smaller scales, not to mention other points of dissimilarity.
• Thesaurus, vol. iii. pi. 34. f. 3.
I.
2 . T e t r a g o n o p t e r u s r u t il u s . Jen.
P l a t e X X III. f i g . 2 .
T . corpore ovali, compressissimo, altitudine tertiam partem longitudinis. M e ad basin
furcoe caudalis mensA, cequante : osse maxillari angusto, retrorsum arcucito : pinna
d o r s a l i subtriangulari, paululumporieventrales exorienti; analiloevi,longâ, altitudine
retro cito decrescente ; utrâque plicis membranaceis, radiis longitudinaliter adkæren-
tibus, instruetà: squamis in lineâ laterali 40, in lineâ inter pinnas ventrales et
dorsalem transversâ 14.
D. 1/9 ; A. 2/27 ; C. 19, &c. ; P . 14 ; V. 8 .
L o n g . u n c . 4 . lin . 3.
FoRM.^Moi-e oval than rhomboidal ; the back and napo not so much elevated as in the last species ;
the profile falling less obliquely. D epth one-third of the entire length, measured to the base
of the caudal fork; head one-fifth of the same. N ot above fourteen scales m the depth, and
forty in the lateral line, which occupies the eighth row from the top. The scales on the whole
similar, but with the basal margin not so straight and regular, and somewhat projecting m the
...iddlo in tho form of a blunt salient angle. T he dorsal commences a trifle nearer the caudal,
and at the middle of the entire length, the caudal alone excluded. T he pectorals reach just to
the insertion of the ventrals, which last are a trifie in advance of the dorsal. T he second anal
spine is longer, and nearly half the length of the soft rays which follow.
C o L O ü i i .— “ Back iridescent greenish brow n; a silver band on the side. Fins dirty orange i^tail
with a central black b and; above and below the band bright red and orange.”—D .—The
colours appear very similar to those of the last species. ^ T he hum eral spot, however, is less
obvious, while, on tho other hand, tho silver band on the side can still be distinguished.
H abitat, Rio Parana, South America.
Taken with the last species, to which it is very closely allied. Mr. Darwin
observes in his notes, that both are among the commonest of the river fry m the
Rio Parana.
Both this and the T . Abramis are distinguished by having narrow longitudinal
folds of skin attached to the basal half of the rays of the dorsal and anal
fins, a character which does not shew itself in any of the three species next to he
described.
3. T e t r a g o n o p t e r u s s c a b r i p i n n i s . Jen.
P l a t e X X III. f i g . 3 .
T . corpore ovali, subelongato, valde compressa; altitudine tertiam partem longitudinis,
caudali exclusâ, cequante : osse maxillari paulo dilatato, recto : pinnâ dorsali sub-
oblongâ, altâ, pone ventrales exorienti; anali scabrd, altitudine retrà gradatim
decrescente ; radiis plicis membranaceis nullis : squamis in lined laterali circiter 38,
in lined inter pinnas ventrales et dorsalem transversâ 12.
D. 1/9; A. 3/22; C. 19, &c. ; P. 13; V. 8.
L o n g . u n c . 3. lin . 7.