124 ZOOLOGY OF THE VOYAGE OF THE BEAGLE. 
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 suborbital 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 striae, and with two 
coloured deeper strie on the free portion diverging from the centre in a V-like form: some 
scales have three or four of these coloured strie, drawn more or less regularly. 
The 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, com- 
mencing 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 line 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 mem- 
branous folds of skin. There are also some small scales along the base of the anal, but 
none apparent on the dorsal. In the axilla of the ventrals is an elongated scale, not half 
their length. 
Cotour.—* 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. 
Habitat, 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 re- 
semblance between it and the species figured in Seba.* It differs from the 7”. 
chalceus of Spix, in its much smaller scales, not to mention other points of dissi- 
milarity. 
* Thesaurus, vol, iii. pl. 34. f. 3, 
