FISH. 115 
Cortour.—Greenish-brown, with a conspicuous black spot on the middle of each side, a little in 
advance of the commencement of the dorsal. Dorsal a little dotted and mottled with dusky, 
especially towards the tips of the rays. The other fins plain. 
Habitat, Rio de Janeiro. 
This species, which was discovered by Humboldt, was observed by Mr. 
Darwin in great numbers in fresh-water ditches at Rio de Janeiro: others were 
taken in equal plenty in a salt lagoon. The bellies of the females are very tur- 
gid when big with young, which are said to be excluded alive, and yellowish.— 
Valenciennes, in his description, speaks of the opercle as being smooth, or with- 
out scales, though he says the preopercle is covered with scales ; and he would 
lead one to suppose that they are absent on this part in the whole genus, as it 
enters into his generic character; I find them, however, present, though very thin 
and transparent, both in this species and the next. 
The general resemblance which Pecilia bears to Mugil, as regards the form 
of the head and mouth, is very striking, and calls up irresistibly the idea of 
some relation of analogy between these two genera. 
2. Pa@ciL1A DECEM-MACULATA. Jen. 
Puatre XXII. Fig. 1. 
P. corpore sub-elongato, viridescenti-fusco ; lateribus maculis nigris circiter decem 
serie longitudinal dispositis; pinnis tmmaculatis: dentibus subincisivis: caudali 
subtruncatd. 
D. 8; A. 10; C. 22, brevibus inclusis; P.9; V. 5. 
Lona. unc. 1. lin. 4. 
Form.—More elongated than the last species; the snout not so acute when viewed laterally. 
Depth not more than one-fifth of the entire length, the length of the head being equal to it. 
Mouth and jaws similar; the teeth also in one row in each jaw, and forming a compact series, 
but more incisor-like than pointed, with oblique cutting edges. Scales of a different form 
and sculpture; more oblong than semi-elliptical, broader than long; the deep strize behind 
more numerous, amounting to twenty or more, and all drawn nearly of the same length. They 
cover all the pieces of the opercle as in the P. unimaculata. 
Dorsal and anal exactly opposite, commencing at a point a little anterior to the middle of 
the entire length, reckoning this to the extremity of the caudal. Caudal rather more ap- 
proaching to square than rounded; the number of rays fewer than in the last species. 
Pectorals narrower, having also fewer rays. Ventrals very small, scarcely more than half 
the length of the pectorals. When laid back, the pectorals reach to beyond the insertion of 
the ventrals: the ventrals do not attain to the anal. 
Cotour.—Greenish-brown, with about ten conspicuous somewhat oval-shaped dusky spots, 
arranged in a longitudinal line along the middle of each side. All the fins plain. 
Habitat, Maldonado. 
This, which is evidently a new species of Pecilia, was taken by Mr. Darwin 
