Pœcilia unimaculata, _Val._ in Humb. Zool. et Anat. Comp. vol. ii. p.
158. pl. 51. fig. 2.
FORM.—Body oval, slightly elongated, thick anteriorly, compressed
behind. The dorsal and ventral lines meeting at the month at an
acute angle; but the head, when viewed from above, broad, and very
much flattened between the eyes, and the snout obtuse. Greatest
depth about one-fourth of the entire length: thickness two-thirds of
the depth. Length of the head nearly equalling, or a little less
than, the depth of the body. Mouth small: jaws very protractile;
each with a single row of very fine, close-set, pointed teeth; the
lower one a trifle the longest. Eyes large, their diameter three and
a half times in the length of the head, high in the cheeks, reaching
to the line of the profile. Nostrils consisting of one small orifice
a little above and rather in advance of the eyes.
Scales large, investing the head and all the pieces of the gill-cover,
though very thin and transparent on the opercle and not very obvious
there. On the body there are about eight in the depth, and
twenty-seven or twenty-eight in a longitudinal row from the
gill-opening to the caudal. One taken from the middle of the side
found to be of a semi-elliptic form, the exposed portion marked with
numerous very fine curved concentric lines, the basal with sixteen
or seventeen deeper-cut nearly parallel striæ gradually lengthening
from the sides towards the middle, but not converging to a fan.
Lateral line very faintly marked out by a dotted line, scarcely
obvious in some places.
Dorsal small, commencing exactly at the middle point of the entire
length, measuring this last quite to the extremity of the caudal.
Anal similar and opposite; in strictness, however, terminating a
very little in advance. The last ray in both these fins double: the
first two in the anal short. Caudal rounded. Pectorals and ventrals
small and narrow, the former three-fourths the length of the head;
the latter not above half the same. The pectorals, when laid back,
reach to the insertion of the ventrals, but the ventrals hardly
reach to the commencement of the anal.
B. 5; D. 7; A. 9; C. about 24, including short ones; P. 14 or 15; V. 6.
Length 2 inches.
[Illustration:
_Fish. Pl. 22._
_From Nature on Stone by W. Hawkins._
]
_N^o. 1. Pœcilia decem-maculata._ _Magnified View twice Natural Size._
_1a._ _Natural Size._
_2. Lebias lineata._ _Nat. Size._
_2a._ _Magnified View of Teeth._
_3. Lebias multidentata_ _Nat. Size._
_3a._ _Magnified View of Teeth._
_4. Mesites maculatus._ _Nat. Size._
_5. attenuates._ „
COLOUR.—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 turgid 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 without 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 _Pœcilia_ 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. PÆCILIS DECEM-MACULATA. _Jen._
PLATE XXII. Fig. 1.
_P. corpore subelongato, viridescenti-fusco; lateribus maculis nigris
circiter decem serie longitudinali dispositis; pinnis immaculatis:
dentibus subincisivis: caudali subtruncatà._
D. 8; A. 10; C. 22, brevibus inclusis; P. 9; V. 5.
LONG. 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 striæ 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 approaching 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.
COLOUR.—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 _Pœcilia_, was taken by Mr.
Darwin at Maldonado, in a lake that had been suddenly drained. There are
three specimens in the collection, none of them exceeding the length
above given. Mr. Darwin, however, states in his notes, that he believes
them to be full grown, having taken them so repeatedly, in brooks, of
the same size. The number of spots varies from nine to twelve, and is
sometimes different on the two sides of the same specimen.
Independently of the spots, which at once characterize this species, it
is readily distinguished from the last by its teeth, which are more
cutting than pointed, and in this respect rather departing from the
character of the genus as established by Valenciennes.
1. LEBIAS LINEATA. _Jen._
PLATE XXII. Fig. 2.
_L. corpore subelongato, subcompresso, viridescenti-fusco; lateribus
lineis circiter septem longitudinalibus nigris, e maculis parvis
subconfluentibus formatis: dentibus uniseriatis: caudali rotundatâ._
D. 9; A. 9; C. 26, brevibus inclusis; P. 13; V. 6.
LONG. unc. 1. lin. 10.
FORM.—General form very similar to that of the _Pæcilia
decem-maculata_. Slightly compressed; the depth one-fifth of the
length; the length of the head about four and a half times in the
same. Head depressed: snout obtuse: mouth small; the commissure
horizontal. Upper jaw very protractile; the lower one rather the
longest, when the mouth is shut. Teeth forming a single closely set
series, somewhat compressed at bottom, the cutting edges tricuspid.
Diameter of the eye nearly one-fourth the length of the head. Some
large conspicuous pores on the lower jaw, passing upwards in a
series along the margin of the preopercle, not very near together,
about eight or nine in all.
Scales large, covering the head and all the pieces of the gill-cover,
as well as the body. About eight in the depth, and thirty in a
longitudinal line from the gill to the caudal. One taken from the
middle of the side of a semi-elliptic somewhat oblong form; the free
portion very finely striated, the basal with ten or twelve
deeper-cut striæ, these last nearly parallel, and of equal lengths.
Lateral line faintly marked out by a dotted line; the first half in
the third row of scales from the top, the last half in the fourth
row.
Dorsal commencing at exactly the middle point of the entire length.
Anal opposite and similar. Caudal rounded. Pectorals small, about
two-thirds the length of the head. Ventrals smaller, barely one-half
of the same. The pectorals, when laid back, reach to the insertion
of the ventrals; but the latter hardly attain to the anal.
COLOUR.—Greenish-brown, with six or seven longitudinal dark lines on
the sides, the lines apparently made up of spots for the most part
confluent, but here and there not so, interrupting the continuity of
the lines. All the fins pale dusky, without any spots or markings.
Habitat, Maldonado.
This new species of _Lebias_ was taken by Mr. Darwin in the same lake at
Maldonado with the _Pœcilia decem-maculata_. There are several specimens
in the collection, none of them exceeding the size above mentioned, and
they have all the appearance of being full grown. Some have the lines of
spots much more interrupted than others.