126 ZOOLOGY OF THE VOYAGE OF THE BEAGLE. 
Form.—Still more oval and elongated than the last species, the profile falling in a gentle curve from 
the dorsal to the end of the snout. Depth exactly one-third of the length, excluding caudal: 
head one-fifth of the entire length, caudal included. Maxillary rather dilated towards the bot- 
tom, and quite straight, not curving backwards as in both the last species. Teeth rather larger, 
and more conspicuous. Nostrils larger. Only twelve scales in the depth, the lateral line 
occupying the seventh row from the top: thirty-seven or thirty-eight in the lateral line. Scales 
of a rather different form; the basal margin more sinuous, the free margin not so regularly 
curved, the coloured striz hardly obvious. Dorsal more oblong than triangular, higher in rela- 
tion to the depth, of which it equals two-thirds, commencing at a point anterior to the middle 
of the length, excluding caudal. The pectorals reach a little beyond the ventrals, which are 
attached a little in advance of the dorsal. The anal has all the rays longer, and more nearly 
equal, the posterior part of the fin not being so much sloped off: there are three spines at the 
commencement, the first two minute, the third not quite half the length of the soft rays: this 
fin is furthermore distinguished from that of the two former species by the rays being set with 
asperities, which communicate a scabrous harsh feel to the touch, when the finger is passed 
along them from the base upwards. 
Cotour.—Not noticed in the recent state. In spirits it appears more silvery than either of the two 
last species: the back and upper part of the sides being brownish. A humeral dusky spot, and 
the remains of what was probably a bright silver band along the middle of the side from the gill 
to the caudal. At the base of the caudal is a dusky spot, which is prolonged in a line along 
the central rays to the commencement of the fork. The other fins faintly edged with dusky, 
but otherwise pale. 
Habitat, Rio de Janeiro. 
The more oval and elongated form, straight maxillary, and scabrous anal fin, 
at once distinguish this species from either of the two last. It was taken by Mr. 
Darwin in fresh water, at Rio de Janeiro, in June. 
4. TETRAGONOPTERUS TENIATUS. Jen. 
T. corpore ovali, valde compresso, altitudine tertiam partem longitudinis, hac ad basin 
furce caudalis mensd, equante: osse maxillari margine posteriore recto: pinnd 
dorsali. supra ventrales accurate exorienti; anali levi, altitudine retro cito 
decrescente ; radiis plicis membranaceis nullis : squamis in lined laterali 40, in linea 
mnter pinnas ventrales et dorsalem transversa 14. 
D. 1/10; A. 3/22, &e. 
Lone. unc. 2. lin. 2. 
Form.—Depth and general form similar to those of the 7. 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 J. 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. 
