Chapter VIII: Part 8

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.

2. LEBIAS MULTIDENTATA. _Jen._

PLATE XXII. Fig. 3.

_L. corpore subelongato, subcompresso, viridescenti-fusco; lateribus
fasciis angustis paucis longitudinalibus albidis obscurioribus:
dentibus seriebus plurimis dispositis, omnibus tricuspidatis:
caudali rotundatâ._

D. 9; A. 9; C. 26, brevibus inclusis; P. 13; V. 6.
LONG. unc. 3. lin. 2.

FORM.—The general form and proportions of this species are extremely
similar to those of the last; but it differs very remarkably in
having behind the anterior row of tricuspid teeth, a band of minuter
teeth above and below, all of which are also tricuspid, and
similarly formed to those in front. Head one-fifth of the entire
length; flattened on the crown. Jaws nearly equal; upper one very
protractile. Scales large; about thirty-two in a longitudinal line,
and eight in the depth; covering all the pieces of the opercle;
similar in form to those of the last species, but with the striæ on
the free portion finer and more numerous, the deep-cut basal striæ
also rather more numerous, amounting to about fourteen, and of
unequal lengths, gradually increasing from the outermost to the
middle ones. Lateral line similar; also the same pores on the lower
jaw. Fins and finray-formula similar: in both species the first and
last rays of the dorsal and anal are simple, and shorter than the
others. The anal perhaps terminates a little nearer the caudal than
the dorsal does.

COLOUR.—(_In spirits._) Greenish-brown, with very little appearance of
markings in its present state. There is, however, some indication of
an irregular scattered row of small black spots on each side, a
little below the ridge of the back; also of two or three pale
longitudinal narrow bands along the middle of the sides, which were
probably more conspicuous in the living fish. The belly is yellow,
and very tumid; but these are evidently characters merely indicative
of the female sex.

Habitat, Monte Video.

This is another new species of _Lebias_ taken by Mr. Darwin in fresh-water at Monte Video, if indeed it strictly belong to the genus; but the circumstance of the teeth being in several rows, and in fact forming a complete band, is at variance with the generic characters as given by Cuvier. The teeth however being exactly of the same form as in the other species, and the general characters on the whole similar, I have not thought it expedient to erect it into a new genus. There is but one specimen in the collection, which appears to be a large female big with young.

GENUS—MESITES. _Jen._

_Corpus elongatum, gracile, antice subcylindricum, postice compressum,
nudum, squamis nullis. Caput depressum. Rostrum breve, obtusum: os
terminale, rictu modico. Maxillæ debiles; superior margine ex
ossibus intermaxillaribus omnino formato, maxillaribus retroductis
et a labio partim celatis. Dentes minuti, acuti, in maxillâ utrâque
uniseriati; in linguâ et vomere biseriati; in ossibus palatinis et
pharyngalibus nulli. Apertura branchialis amplissima, membranâ
sex-racliatâ, subter gulam profundè emarginatâ, haud isthmo annexâ.
Pinnæ dorsalis et analis valde retropositæ, oppositæ. Pinnæ
pectorales et ventrales parvæ. Pinna caudalis leviter emarginata._

There can be no doubt, I imagine, as to this being an entirely new form, and a very interesting one, from the circumstance of its being at the extreme end of the family to which it belongs, and its very much departing from the usual characters of that family. I have referred it to the _Cyprinidæ_, taking that group in the enlarged view in which Cuvier accepts it; though by those who divide it into subfamilies it would probably be associated with the _Cobitidæ_, or made to constitute a distinct one by itself. It agrees with the _Cyprinidæ_ in general in the form of its mouth, in the upper jaw having its margin entirely formed by the intermaxillary, the maxillary being present, but placed behind and partly concealed in the thickness of the lip, and in the want of an adipose; but it altogether departs from that family in the entire want of scales, of which there is not even a vestige in the dried skin, and in which respect it would seem to shew an affinity to the _Siluridæ_. Yet it has none of the other characters of the family just mentioned. On the other hand, in the backward position of the dorsal and anal fins, which are opposite to each other, it agrees with the _Esocidæ_. The pharyngeal bones are unarmed, but this deficiency is made up for by the strong curved teeth on the tongue, independently of the minuter ones in the jaws.

The intestine is extremely short and quite straight, measuring only fourteen lines in length from the pylorus to the anus, in a specimen two inches and a half long. The stomach is of an oval form, of considerable capacity, very membranaceous, with the cardiac and pyloric openings near together at the upper extremity, from the latter of which the intestine is immediately reflexed to pass off to the anus. In the specimen dissected, the stomach was much distended by a nearly perfect individual of the genus _Colymbetes_, which appeared to have been recently swallowed, and was scarcely at all altered. There are no cœcal appendages. The air-bladder is of an elongated oval form, and of considerable development.

Mr. Darwin’s collection contains no less than three species of this new genus, differing but slightly from each other. Two are from the most southern parts of South America, the third from New Zealand.

1. MESITES MACULATUS. _Jen._

PLATE XXII. Fig. 4.

_M. viridescenti-fuscus; dorso et lateribus maculis crebris, hic et
illic confluentibus, nigris; ventre niveo; pinnarum radiis
nigro-punctatis._

B. 6; D. 10; A. 16; C. 16, &c.; P. 12; V. 7.
LONG. unc. 2. lin. 8.

FORM.—Slender and very much elongated. Body anteriorly subcylindrical,
compressed behind. Greatest depth not more than one-eighth of the
entire length: thickness about three-fourths of the depth. Head
rather depressed, about one-sixth of the entire length. Snout short
and rounded; mouth at the extremity; the gape moderate, not quite
reaching to beneath the anterior angle of the eye. Lower jaw
ascending a little to meet the upper, and, when the mouth is open,
appearing rather the longest. Intermaxillary fixed, forming the
entire margin of the upper jaw, the maxillary being behind it, and,
though of nearly equal development, not very distinct: both bones
slender. Teeth small, but sharp-pointed, rather widely apart,
arranged in a single row along the edge of the intermaxillary, and
in the lower jaw; the series above consists of about eighteen, that
below of about twenty-one: also a double longitudinal row on the
tongue, each row containing five or six teeth, the anterior ones
curved, and larger than any of those in the jaws: a similar double
row, but of minuter ones, down the middle of the vomer; none,
however, on the palatines or pharyngeans. Eyes rather large, their
diameter contained about three and a half times in the length of the
head, distant scarcely one diameter from the end of the snout. The
nostrils appear to consist of only a single aperture in front of the
eye, in the neighbourhood of which, and also above the eye, are
several large pores. The opercle and subopercle taken together
approach to an oblong form, the posterior margin being straight and
nearly vertical: the subopercle is not much developed, nor very
distinct. Gill-opening very large, the membrane thick, with six
rays, deeply notched beneath, and not fastened down. The whole skin
is perfectly smooth and naked, invested with mucosity. No appearance
of any lateral line, unless a fine dark streak be so called, passing
along the middle of the sides, and dividing them into two equal
parts.

The dorsal and anal are opposite to each other, and both placed very
far back, almost at the extremity of the body. They commence in
nearly the same vertical line, a very little anterior to the
commencement of the last third of the entire length; but the anal
being longer than the dorsal, it extends nearer the caudal. The form
of these fins is much as in the genus _Cobitis_. The dorsal has the
first three rays simple, the rest branched: the anal also has the
first three simple, the first very short. Caudal about one-eighth of
the entire length, with a shallow notch, the principal rays
branched. The vent is just before the anal. The ventrals arise from
about the middle of the entire length, the distance from their
insertion to the commencement of the anal being twice their own
length. The pectorals are small, and rather narrow, equalling about
two-thirds the length of the head or hardly so much: they are
attached low down, but not quite so low as in the genus _Cobitis_.

COLOUR.—(_In spirits._) Greenish-brown, with numerous conspicuous
spots and small irregular transverse bars of black. Under a lens the
spots appear to be made up of thickly crowded black specks upon a
dark brown ground: the bars result from some of the spots being
confluent. The belly appears to have been white. The rays of all the
fins are dotted with dusky, but the membranes transparent and
colourless.

The individual described above was taken by Mr. Darwin in a fresh-water brook, in Hardy Peninsula, Tierra del Fuego. His collection, however, contains four other specimens found in streamlets and creeks high up the river of Santa Cruz in Patagonia, where they are said to have been numerous. Though these last are slightly different, they are evidently referable to the same species: they also vary a little from each other. Their peculiarities are as under:

The largest measures 2 inches 8 lines in length, and has the following fin-ray formula:

D. 12; A. 16; C. 16, &c.; P. 14; V. 7.

The next in size is 2 inches 6 lines, with the fin-ray formula thus:

D. 11; A. 16; C. 16, &c.; P. 13; V. 7.

These specimens agree in being both slenderer than the one from Tierra del Fuego. The depth is eight and a half, if not nine times in the entire length: the head rather more than one-sixth of the same. The colours are similar, except that the spots are not quite so numerous, and of a more regular form, seldom running together to form bars.

It is to these specimens that Mr. Darwin’s notes refer, respecting the colours of this species in the recent state. As follows: “Pale greenish brown, with small irregular transverse bars of black; belly snow white.”—D.

The third of the Patagonian specimens is 2 in. 2 lin. long. Fin-ray formula—

D. 10; A. 15; C. 16, &c.; P. 14; V. 7.

The fourth is of the same length.

D. 11; A. 15; C. 16, &c.; P. 13; V. 7.

These last two specimens are exactly similar to each other in colours, but differ from the former two in being almost immaculate, having only a few spots on the upper part of the back. This brings them very close to the following species, from which they are scarcely to be distinguished, except by their smaller eyes. It should be observed further, that the fleshy part of the tail in these specimens has the upper and under edges fringed with the short accessory rays of the caudal, a character which is not so obvious in any of the others.

2. MESITES ALPINUS. _Jen._

_M. viridescenti-fuscus, dorso saturatiore; hoc, et lateribus, et
pinnis, nigro levissimè irroratis, immaculatis; ventre niveo; oculis
majusculis._

D. 10; A. 16; C. 16, &c.; P. 13; V. 7.
LONG. unc. 2. lin. 5.

FORM.—Very little difference in form between this and the last
species. The eyes, however, are decidedly larger, measuring in
diameter one-third the length of the head. The head itself also
appears somewhat longer, being nearly one-fifth of the entire
length. The anterior teeth on the tongue do not seem much larger
than the others. Fins similar.

COLOUR.—(_In spirits_). Greenish-brown, deepening in tint at the top
of the back. Back, sides, and fins, immaculate, but thickly powdered
with minute dark specks, scarcely visible except under a lens. These
specks give the fins a more dusky appearance than they possess in
the last species. The belly appears to have been white.

A _second specimen_ does not differ from the above in any respect,
except in being rather smaller, and scarcely more than two inches in
length.

Habitat, Tierra del Fuego.

This species was taken by Mr. Darwin in alpine fresh-water lakes in Hardy Peninsula, Tierra del Fuego. I have no hesitation in considering it distinct from the last, as there are two specimens exactly similar, both shewing a larger eye, and an entire absence of all approach to spots; while the whole surface of the back and sides is thickly irrorated with dark specks, a character which does not appear in the plain varieties of the _M. maculatus_.

3. MESITES ATTENUATUS. _Jen._
PLATE XXII. fig. 5.

_M. viridescenti-fuscus, ventre vix pallidiore; dorso, et lateribus,
pinnarumque radiis, sparsim nigro levissimè irroratis, immaculatis:
corpore prægracili, anticè attenuato; capite et oculis minoribus._

D. 11; A. 17; C. 16, &c.; P. 12; V. 7.
LONG. unc. 2. lin. 6.

FORM.—Rather more slender than either of the last two species, the
body more attenuated anteriorly; the head also smaller, though
scarcely shorter. Mouth and eyes both smaller; the diameter of the
latter not more than one-fourth of the length of the head. Teeth
also rather more minute as well as more numerous. The fins are
similar, except that the ventrals appear to stand rather more
forward, being attached exactly in the middle of the entire length,
excluding caudal: the distance from their insertion to the
commencement of the anal is more than twice their own length. The
outer rays of the caudal are worn, but there was probably a shallow
notch when entire: the short accessory rays are very numerous, and
form a very distinct fringe along the upper and lower edges of the
fleshy part of the tail.

COLOUR.—(_In spirits._) Greenish-brown, much more uniform than in
either of the last two species, not deepening on the back, and
scarcely becoming paler underneath. The back sides, and rays of the
fins, are finely irrorated with dusky specks, as in the _M.
alpinus_, but not to the same extent, the specks being more thinly
scattered, and here and there scarcely visible. From the same cause
the fins appear paler.

Habitat, Bay of Islands, New Zealand.

This, which is a very distinct species of this new genus, was taken by Mr. Darwin in fresh-water in the Bay of Islands, New Zealand. It is well characterized by its more attenuated head and smaller eye, than those of either of the two others.

FAMILY.—ESOCIDÆ.

EXOCŒTUS EXSILIENS. _Bl.?_

Exocœtus exsiliens, _Bl._ Ichth. pl. 397.

FORM.—Head about one-sixth of the entire length, and approaching to
the form of a parallelopiped; very much flattened on the crown and
between the eyes quite to the end of the snout, broader above than
beneath, so that the cheeks are beyond the vertical inclining inwards
at bottom. Snout short: mouth not much cleft; when shut, the jaws are
equal, and the commissure of the lips appears to extend to beneath the
anterior margin of the eye, but the maxillary, which retires
completely beneath the suborbital, does not reach so far: when the
mouth is open, the maxillary becomes vertical, and the intermaxillary
being scarcely at all protractile, the lower jaw is a little the
longest. Teeth very minute: a row, scarcely visible, along the
forepart of the intermaxillary, but not extending to the sides of the
jaw: none that can even be felt in the lower jaw, or in any other part
of the mouth. Tongue rounded, and free at the tip. A loose veil of
skin hangs down in front of the palate, from immediately behind the
teeth in the upper jaw. Eyes round, and very large; the upper part of
the orbit reaching to the line of the profile, and forming a slightly
salient ridge: their diameter very nearly one-third the length of the
head; between them and the end of the snout is two-thirds of a
diameter; the distance from one to the other across the crown is one
diameter and a quarter. The nostrils consist of one large round
orifice a little in advance of the eyes. The membrane of the opercle
forms a slightly salient angle backwards, near the upper part of the
gill-opening. Scales large, of a somewhat irregular form, approaching
to oblong, nearly twice as broad as long, the posterior margin with
three or four incisions near the middle, and a few rather indistinct
nearly parallel striæ on the surface of the basal portion; in others
these striæ converge to form a small but very regular fan; and the
scales appear to vary a good deal on different parts of the body.

_Fish. Pl. 23._

_B. Waterhouse Hawkins del._
]

_N^o. 1. Tetragonopterus Abramis._ _All Nat. Size._
_2. rutilus._ „
_3. scabripinnis._ „
_4. interruptus._ „
_1a. 2a. 3a. 4a. Magnified View of Teeth._

The pectorals reach exactly to the base of the lateral caudal rays;
the first two rays are simple, and all the others branched; first ray
of all not half the length of the fin. Dorsal so situate as to leave a
space between it and the end of the fleshy part of the tail about
equal to its own length; the first ray simple, the others branched;
the last prolonged beyond those which immediately precede it so as to
form rather a point backwards. Anal similar to the dorsal, and
answering to it exactly. The ventrals are attached at a point, in this
specimen, about half an inch posterior to the middle of the entire
length, reckoning this to the end of the fleshy part of the tail; but
are not much out of the middle, if the length be reckoned to the end
of the upper lobe of the caudal: their length is contained not quite
three and a half times in the entire length, excluding caudal; and
they reach exactly to the end of the dorsal and anal: first ray very
much branched, and only one-third the length of the fin; second ray
appearing like two or even three rays at its upper extremity, from the
circumstance of the several branches of it being of unequal length;
all the other rays branched likewise. Vent a very little in advance of
the anal. Upper lobe of the caudal one-third shorter than the lower;
this last being exactly the same length as the ventrals.

D. 11; A. 12; C. 16, &c.; P. 18; V. 6.
Length 12 inches 8 lines.

COLOUR.—The colours were not noticed in the recent state; and the
specimen is in such bad condition, and so much altered by the
spirit, that they are now no longer distinguishable.

The flying-fish above described was taken by Mr. Darwin in the Pacific Ocean, off the coast of Peru, in Lat. 18° S. It appears to be the _E. exsiliens_ of Bloch, but as I am not aware that the species of _Exocœtus_ have been ever rigourously worked out, and closely compared from different parts of the globe, I have thought it expedient to annex a description, by which it may be identified, if it prove hereafter distinct.[34]

FAMILY.—SALMONIDÆ.

1. TETRAGONOPTERUS ABRAMIS. _Jen._

PLATE XXIII. fig. 1.

_T. corpore subrhomboideo, compressissimo, altitudine fere dimidium
longitudinis, pinnâ caudali exclusâ, æquante: osse maxillari
angusto, retrorsum arcuato: pinnâ dorsali triangulari, suprâ
ventrales accuratè exorienti; anali lævi, longâ, altitudine retrò
cito decrescente; utrâque plicis membranaceis, radiis
longitudinaliter adhærentibus, instructâ: squamis in lineâ laterali
46, in lineâ inter pinnas ventrales et dorsalem transversâ 17._

B. 4; D. 1/10; A. 2/30; C. 19, &c.; P. 13; V. 8.
LONG. unc. 4. lin. 7.

FORM.—Of a subrhomboidal form, the nape and back being much elevated,
whence the profile falls very obliquely and in nearly a straight
line. Greatest depth nearly half the entire length, excluding
caudal. Body very much compressed, the thickness being nearly three
and a half times in the depth. Head approaching to a laterally
flattened cone, with the length and height nearly equal. Snout very
short; mouth but little cleft; when open, the lower jaw projecting
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 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.

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, 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 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 membranous folds of skin. There are
also some small scales along the base of the anal, but none apparent
on the dorsal. In the axillæ of the ventrals is an elongated scale,
not half their length.

COLOUR.—“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 resemblance between it and the species figured in Seba.[35] It differs from the _T. chalceus_ of Spix, in its much smaller scales, not to mention other points of dissimilarity.

2. TETRAGONOPTERUS RUTILUS. _Jen._
PLATE XXIII. fig. 2.

_T. corpore ovali, compressissimo, altitudine tertiam partem
longitudinis, hâc ad basin furcæ caudalis mensâ, æquante: osse
maxillari angusto, retrorsum arcuato: pinnâ dorsali subtriangulari,
paululum pone ventrales exorienti; anali lævi, longâ, altitudine
retrò cito decrescente; utrâque plicis membranaceis, radiis
longitudinaliter adhærentibus, instructâ: 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.
LONG. unc. 4. lin. 3.

FORM.—More oval than rhomboidal: the back and nape not so much
elevated as in the last species; the profile falling less obliquely.
Depth one-third of the entire length, measured to the base of the
caudal fork: head one-fifth of the same. Not above fourteen scales
in 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 in the middle in the form of a blunt salient angle. The
dorsal commences a trifle nearer the caudal, and at the middle of
the entire length, the caudal alone excluded. The pectorals reach
just to the insertion of the ventrals, which last are a trifle in
advance of the dorsal. The second anal spine is longer, and nearly
half the length of the soft rays which follow.

COLOUR.—“Back iridescent greenish brown: a silver band on the side.
Fins dirty orange: tail with a central black band; above and below
the band bright red and orange.”—D.—The colours appear very similar
to those of the last species. The humeral spot, however, is less
obvious, while, on the other hand, the silver band on the side can
still be distinguished.

Habitat, 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 in 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 be described.

3. TETRAGONOPTERUS SCABRIPINNIS. _Jen._

PLATE XXIII. fig. 3.

_T. corpore ovali, subelongato, valde compresso; altitudine tertiam
partem longitudinis, caudali exclusâ, æquante: osse maxillari paulo
dilatato, recto: pinnâ dorsali suboblongâ, altâ, pone ventrales
exorienti; anali scabrâ, altitudine retrò gradatim decrescente;
radiis plicis membranaceis nullis: squamis in lineâ laterali
circiter 38, in lineâ inter pinnas ventrales et dorsalem transversâ
12._

D. 1/9; A. 3/22; C. 19, &c.; P. 13; V. 8.
LONG. unc. c. 3. lin. 7.

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 bottom, 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 striæ hardly obvious. Dorsal more oblong than
triangular, higher in relation 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.

COLOUR.—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 TÆNIATUS. _Jen._

_T. corpore ovali, valde compresso, altitudine tertiam partem,
longitudinis, hâc ad basin furcæ caudalis mensá, æquante: osse
maxillari margine posteriore recto: pinnâ dorsali suprà, ventrales
accuratè exorienti; anali lævi, altitudine retrò cito decrescente;
radiis plicis membranaceis nullis: squamis in lineâ laterali 40, in
lineâ inter pinnas ventrales et dorsalem transversâ 14._

D. 1/10; A. 3/22, &c.
LONG. unc. 2. lin. 2.

FORM.—Depth and general form similar to those of the _T. 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 _T.
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.

COLOUR.—Much as in the _T. scabripinnis_. The same silver band, only
more brilliant; also the same humeral spot, and the spot at the base
of the caudal extending along the middle rays.

Habitat, Rio de Janeiro.

The above description is that of two small specimens, similar to each other, obtained by Mr. Darwin in a running brook at Socego, in the province of Rio de Janeiro. They are probably not full grown; but so evidently distinct from either of the last two species, the characters of which are in some measure combined in them, that I have not hesitated to give them a separate place. The silver band is more or less obvious in all the species of this genus brought home by Mr. Darwin, but it is much brighter in this than in any of the others.

5. TETRAGONOPTERUS INTERRUPTUS. _Jen._
PLATE XXIII. fig. 4.

_T. corpore ovali, valde compresso: altitudine tertiam partem
longitudinis totius æquante: ore parvo; osse maxillari brevissimo,
dilatato, margine posteriore recto: dentibus minutis,
multicuspidatis: dorsali subtriangulari, pone ventrales exorienti;
anali (in uno sexu?) scabrâ, altitudine retrò subito decrescente;
his pinnis plicis membranaceis nullis: squamis in lineâ
longitudinali 35, in lineâ inter pinnas ventrales et dorsalem
transversâ 10: lineâ laterali interruptâ, haud finem pinnæ
pectoralis attingente._

D. 1/10; A. 2/18; C. 18, &c.; P. 11; V. 7.
LONG. unc. 2. lin. 8.

FORM.—Oval, and not very dissimilar in general form to the _T.
rutilus_, but rather more elevated above the shoulder. Depth exactly
one-third of the entire length: head one-fourth of the same, caudal
excluded. Profile not exactly straight, but very slightly hollowed
out at the crown, then as slightly protuberant above the eyes,
whence it falls more rapidly in front, giving the snout a short and
blunt appearance. Mouth much smaller than in any of the preceding
species, owing to the extreme shortness of the maxillary, which is
broad, with the anterior margin curving outwards, but the posterior
one straight. Teeth very small; the points on the cutting edges
numerous (five or six on each tooth) and nearly equal; apparently
only one row on the intermaxillary, and the same in the lower jaw;
none on the maxillary. Eyes and nostrils as in the other species,
but the anterior orifice of the latter larger. Subopercle much
larger, forming a greater portion of the gill-flap. Scales
relatively larger; only ten in the depth, and thirty-five in the
length. They have no deep striæ on the basal portion, and
consequently no fan; but they are very regularly marked with the
usual finer striæ concentrically arranged, except on the free
portion where they become indistinct.

The lateral line occupies the sixth row of scales from the top, but is
very soon interrupted, coming to an end before it has reached the
length of the pectoral, and not carried over more than eight or nine
scales in the length. Dorsal subtriangular, commencing exactly at
the middle of the length, caudal excluded. Anal shorter than in the
other species, and not reaching so near the caudal; two spines, but
the first extremely minute. Caudal forked for half its length, the
lobes equal. Ventrals more forward than in the other species,
decidedly in advance of the dorsal, and attached at one-third of the
entire length; their axillary scale very small. Pectorals narrow,
reaching beyond them. No long folds of skin accompanying the rays of
the vertical fins.

COLOUR.—Not noticed in the recent state, in which, judging from its
appearance in spirit, it was probably silvery, or perhaps golden,
with somewhat of an olivaceous hue becoming deeper on the back.
There are evident remains of a bright longitudinal lateral band:
also of a black spot at the base of the caudal. The dorsal and the
anterior portion of the anal incline to dusky: the pectorals and
ventrals are slightly dusky at their extremities; there is also a
large irregular dusky stain on the back and shoulders anterior to
the dorsal fin.

A _second specimen_ differs from the above in being a trifle smaller,
and not quite so deep in the body. The anal is also decidedly
scabrous, as in the _T. scabripinnis_, and has one ray less in it.
The colours are similar, excepting that the fins are rather less
dusky, and the large dusky stain on the back and shoulders is
wanting.

Habitat, Maldonado.

This species is one of several that were taken by Mr. Darwin at Maldonado, in the lake that had been suddenly drained, before alluded to. It is immediately distinguished from all the others in this genus above described, by its small mouth and abbreviated lateral line. The circumstance of the anal fin being scabrous in only one of the specimens leads to the suspicion that this may be a sexual character, perhaps common to this and several species; and, judging from its somewhat less depth, I conceive the specimen so distinguished in this instance to be a male.

HYDROCYON HEPSETUS. _Cuv._

Hydrocyon hepsetus, _Cuv._ Reg. An. (ed. 2) tom. ii. p. 312. ———— falcatus, _Freycinet_, (Voyage) Zoologie, p. 221, pl. 48. fig. 2.

FORM.—Back rising slightly from the nape, whence the profile in front
falls obliquely in nearly a straight line to the mouth. Depth
contained about three and a half times in the length, caudal
excluded. Both head and body much compressed, the greatest thickness
being only two-fifths of the depth. The length of the head equals
the depth of the body. Snout appears rather pointed when the jaws
are shut; when open, the lower jaw is a little the longest. Gape
considerable. Maxillary long, commencing before the eyes, and
reaching to a vertical from the posterior part of the orbit;
inclining downwards, lapping obliquely in part over the lower jaw,
gradually widening towards the posterior extremity, which is rather
obliquely rounded. Intermaxillary with two sharp canines in front,
then on each side four or five very small hooked teeth, then another
large canine, though not so large as those in front; behind this
commences the maxillary, which is armed all along its margin with a
regular row of small equal hooked teeth, resembling sharp
serratures; a similar row on each palatine, but none on the vomer or
tongue; this last pointed, and free at the tip. Lower jaw with two
strong canines in front, larger than those in the upper, and fitting
into two holes above, when the mouth is shut; on each side of these
are three only half their size, but increasing backwards, placed at
rather wide intervals; then follow a row of close, minute, sharp
teeth, similar to those on the edge of the maxillary. Eyes rather
large, their diameter not quite one-fourth the length of the head,
distant one diameter and a quarter from the end of the snout.
Suborbital large, consisting of three pieces. Preopercle
rectangular. A row of pores, not very distinct, along the under part
of the lower jaw, thence continued along the limb of the preopercle.
Opercle and subopercle taken together with the posterior margin
forming a slight but regular curve, with scarcely any salient angle.

Head naked; scales on the body of moderate size, arranged in somewhat
oblique rows, especially below the lateral line; one from the middle
of the side below the lateral line of an irregularly rounded form,
the posterior margin rather sinuous, the disk with numerous fine
concentric striæ, but no deeper-cut striæ on the basal portion.
About sixteen scales in a vertical row, and fifty-seven or
fifty-eight in the lateral line: this last bending downwards in a
curve which falls below the middle of the depth. Scales on the
lateral line not larger than the others.

The dorsal answers to the space between the ventrals and anal; its
height equals the depth to the lateral line. Anal long, commencing
exactly under the last ray of the dorsal; the first part of this fin
as high as the dorsal, but the rays, beyond the fifth, gradually
decreasing; three spines, the first two very minute; the last soft
ray double. Caudal in this specimen injured. Adipose and last ray of
the anal in the same vertical line. Pectorals two-thirds the length
of the head, attached very low down beneath the terminating portion
of the gill-flap, narrow and slightly falcate, reaching to the
ventrals, which last are one-fourth shorter. A long narrow scale in
the axilla of each ventral one-third the length of the fin itself.

B. 4; D. 11; A. 3/26; C. 22, &c.; P. 12; V. 8.
Length 4 inches 3 lines.

COLOUR.—“Bluish silvery.”—D.—Some appearance of a dusky spot at the
base of the caudal prolonged in a line along the middle rays, but
scarcely any trace of a humeral one. The dorsal and anal incline a
little to dusky.

Taken at Maldonado, in a fresh-water lake, in June. I have scarcely any doubt of its being the _H. falcatus_ of the Zoology of Freycinet’s voyage, the figure of which it exactly resembles, excepting that the humeral dark spot, if it ever existed, and which is not mentioned in Mr. Darwin’s notes, is now almost entirely effaced. It is probable, however, that there are two or three species nearly allied, for which reason I have been the more particular in my description. The _H. Hepsetus_ of D’Orbigny[36] appears to differ from the _H. falcatus_ of Freycinet (with which last Cuvier associates his name of _Hepsetus_,) in having the lateral line curving upwards rather than downwards, and the caudal fascia as well as the humeral spot more marked. The _Salmo falcatus_ of Bloch is probably distinct from both.

GENUS.—APLOCHITON. _Jen._

_Corpus elongatum, compressum, subfusiforme, undique nudum alepidotum.
Caput parvum. Rostrum breviusculum, subacutum. Os terminale, rictu
modico. Maxilla superior margine ex ossibus intermaxillaribus omnino
formato, maxillaribus, hæc subæquantibus, retroductis. Dentes
minuti, acuti, in maxillâ utrâque uniseriati, in linguâ et vomere
longitudinaliter biseriati, in ossibus palatinis nulli. Apertura
branchialis amplissima, membranâ triradiatâ, subtus profundè
emarginatâ. Pinnæ, dorsalis paululum pone ventrales, analis paululum
pone dorsalem reclinatam, exorientes. Ventrales appendicibus
axillaribus nullis. Pinna caudalis bifurca._

I have already noticed a remarkable new form among the _Cyprinidæ_ brought home by Mr. Darwin, and differing from all the known genera in that family by the entire absence of scales. The one now to be described is not less remarkable among the _Salmonidæ_, and, what is particularly interesting, would seem to occupy an exactly analogous place in this family, departing from it in the same important character of having the skin perfectly naked and free from scales. There are, however, many other points of similarity between _Mesites_ and the genus which I have here termed _Aplochiton_.[37] In both there is the same form of mouth, the margin of the upper jaw being entirely formed by the intermaxillary, behind which is the maxillary of nearly equal development. The teeth in the jaws are similar, both in regard to form and arrangement; there is also the same double longitudinal row on the tongue, and along the vomer. The pieces of the opercle are similar, and the gill-opening equally large in both genera, though the branchial membrane has twice the number of rays in _Mesites_ that it has in _Aplochiton_. Furthermore, the fins are on the whole very similar, with the exception of the dorsal not being so far back in _Aplochiton_, and there being also an adipose in this genus. It is also deserving of notice that both these new forms, so resembling each other in many of their characters, come from the same quarter of the globe, being found either in the most southern parts of S. America, or in the neighbouring islands.

From the circumstance of the naked skin, _Aplochiton_ might by some be referred to the _Siluridæ_, but what was said of the genus _Mesites_ may be repeated here, that it has none of the other external characters of that family. The maxillary, instead of being reduced to a mere vestige, or lengthened into a barbule, is as much developed as in any of the _Cyprinidæ_, and of the usual form; the subopercle also is very distinct;[38] while there is no strong spine at the commencement of either the dorsal or pectoral fins. At the same time it must be mentioned that _Aplochiton_ agrees with the _Siluridæ_ in having no cœcal appendages, though the air-bladder is similar to that of the ordinary _Salmonidæ_. There are some peculiarities connected with the anal and sexual orifices which I shall notice presently, along with other points in the internal structure, in the species to be described first.

_Fish. Pl. 24._

_Waterhouse Hawkins. del._
]

_1. Aplochiton Zebra. Nat. Size._
_1a. Magnified show of anal and generative orifices._
_2. Aplochiton tæniatus. Nat. Size._

Mr. Darwin has brought home two species of this new genus, agreeing precisely in form, but very distinct in respect to size and colouring.

1. APLOCHITON ZEBRA. _Jen._

PLATE XXIV. Fig. 1.

_A. obscurè plumbeus; fasciis nigris transversis: maxillis æqualibus._

B. 3; D. 11; A. 2/14; C. 16, &c.; P. 18; V. 7.
LONG. unc. 9. lin. 6.

FORM.—General form somewhat resembling that of the _Mackarel_,
elongated, and approaching to fusiform. Greatest depth about the
middle, equalling one-sixth of the entire length. Line of the back
and profile nearly straight, the latter falling very little.
Greatest thickness rather more than half the depth. Head small,
contained about five and a half times in the entire length. Snout
short, but rather acute. Mouth with a moderate gape reaching to
beneath the anterior angle of the eye: when shut, both jaws equal,
the lower one ascending at an angle of 45° to meet the upper; when
open, the lower one a little the longest. Margin of the upper jaw
formed by the intermaxillary, the maxillary appearing behind it. A
single row of small but sharp teeth extending along the entire
margins of both jaws: a double row of similar teeth, but stronger
and more curved, down the middle of the tongue; also a double row
along the middle of the vomer. Eyes moderate; their diameter four
and a half times in the length of the head; distant about one
diameter and a quarter from the end of the snout, and with an
interval between them of about one and a half. Nostrils with two
orifices, both roundish, one before the other, with a little
interval between, the posterior one rather the largest. Two distinct
pores on each side of the crown, one behind the other with an
interval between, above and rather behind the eyes. Gill-opening
very large, the membrane with only three flattened rays, deeply
notched beneath, the notch reaching to beneath the middle of the
eyes. All the pieces of the opercle present, but the interopercle
only just appearing behind the angle of the preopercle, and the
subopercle forming but a narrow lanceolate lamina beneath the true
opercle, which last constitutes the greater portion of the
gill-flap, and is of an oblong form, the posterior margin being cut
straight and vertical.

The whole skin perfectly naked everywhere, without the least vestige
of scales. No lateral line, except a faint streak, passing along the
middle of the sides, be so called. Dorsal commencing at the middle
of the length, this last being measured to the base of the caudal
fork; of the same form as in the ordinary species of the genus
_Salmo_; its greatest height a little exceeding its length, which
last is rather more than half the depth of the body; first ray
simple, the rest branched. Adipose small, and just half-way between
the end of the dorsal and the base of the caudal. Anal of a somewhat
triangular form, the margin sloping very much off backwards,
commencing a little beyond the tip of the reclined dorsal, and
terminating opposite the adipose, or perhaps a trifle beyond it; two
small spines at its commencement; the first two soft rays simple,
the others branched. Caudal forked for half its length, the lobes
equal; the whole fin contained about six and a half times in the
entire length; the accessory rays very numerous, and partially
fringing the upper and lower edges of the tail. Pectorals attached
behind the gill-opening, rather below the middle, about two-thirds
the length of the head, of a somewhat triangular form, the rays
gradually shortening from the first, which is the only one
unbranched. Ventrals attached a very little in advance of the
dorsal, rounded, or almost cut square at the ends, the rays being
all nearly equal. They are scarcely shorter than the pectorals: the
space between their insertion and the commencement of the anal is
nearly double their own length. There is no long scale or appendage
of any kind in their axillæ.

COLOUR.—“Dull leaden colour.”—D.—In spirits it appears brown. The
sides are banded with some irregular transverse zebra-like marks,
not noticed by Mr. Darwin, reaching from the back down two-thirds or
three-fourths of the depth, some terminating sooner than others. All
the fins brownish.

Habitat, Falkland Islands.

Mr. Darwin obtained three specimens of this remarkable fish all precisely similar, from a fresh-water lake in the Falkland Islands, in March. The lake was not far from the sea, and connected with it by a brook. He adds in his notes that the species is common there; that it is good eating, and grows to be about half as large again as the individuals procured.

One of these specimens was dissected by Mr. Yarrell and myself, and presented the following internal characters, which are of importance to be noted. The coats of the stomach were thick and muscular; the œsophageal portion with prominent longitudinal plicæ. Its contents, so far as they could be ascertained, consisted of the remains of caddis-worms. The intestine was large, without any cœcal appendages, but with one spiral convolution at the end of the first third of its length from the pyloric orifice: the entire length of the canal was four inches. The air-bladder was large, undivided, and of the same general form as in many of the _Salmonidæ_. There were two elongated flattened lobes of roe nearly ready for exclusion. The anal and sexual orifices were separated, but enclosed in a tubular sheath, common to both, directed backwards; the sheath itself lying in a groove in the abdomen, and five-eighths of an inch in length: the opening to the cavity of the abdomen and sexual organs was at the extreme end of this sheath, and partly closed by two lateral valves; the opening to the intestine, three-eighths of an inch short of the extremity.

2. APLOCHITON TÆNIATUS. _Jen._

PLATE XXIV. Fig. 2.

_A. olivaceus, punctis fuscis minutissimis irroratus; lateribus vittâ
longitudinali argenteâ: maxillâ inferiore longiore._

B. 3; D. 12; A. 2/13; C. 16, &c.; P. 18; V. 7.
LONG. unc. 3. lin. 10.

FORM.—A much smaller species than the last, but the general form
similar. Rather more elongated, the depth being contained seven and
a half times in the length. Head one-fifth of the length measured to
the base of the caudal fork. Snout a little longer, and more
pointed. Lower jaw at all times a little the longest. Teeth similar,
and similarly disposed. Nostrils similar; but no pores on the crown,
or only one on each side, and that not very distinct. All the fins
similar.

COLOUR.—Not noticed in the recent state. In spirits it appears of a
uniform greenish or olivaceous brown, the back and sides very
minutely dotted with darker brown. There is a pale silver band along
the middle of the side, not bounded, however, by any definable line,
but shading off insensibly into the brown above and below. The
irides are still bright, and appear to have been golden.

Habitat, Goree Sound, Tierra del Fuego.

There are three specimens of this second species in the collection, all of the same size, and not differing in any respect from each other, except that one of them has thirteen rays in the dorsal fin, and fourteen soft rays in the anal. Mr. Darwin’s notes state that they were taken at Goree Sound, Tierra del Fuego, in the mouth of a fresh-water stream, where the water was quite fresh; and that when put into salt water they immediately died.

The silver band at once distinguishes this elegant species from the last, independently of its smaller size. The specimens appear full grown.

There is the same peculiarity with respect to the anal and sexual orifices in this species, as in the one previously described.

FAMILY.—CLUPEIDÆ.

1. CLUPEA FUEGENSIS. _Jen._

Mr. Darwin’s collection contains a single individual of a species of Clupea from Tierra del Fuego so extremely similar to the young of the common Herring, that it might almost be mistaken for it. As it is small, and in not very good preservation, I shall merely point out some of its leading characters.

Depth of the body the same as in a young _Herring_ of the same size.
Belly carinated, but with the serratures not more developed than in
that species. Teeth the same, and very minute. The maxillary does not
slope inwards quite so much at its upper extremity, before uniting
with the intermaxillary; but the mouth and its several parts are in
all other respects similar. The same may be said of the pieces of the
opercle, excepting that there is a more sensible notch near the upper
part of the posterior margin of the gill-flap, much as in the common
_Sprat_. It differs also from the Herring in having the ventrals
exactly in a line with the commencement of the dorsal, this last being
placed a little further back than in that species.

D. 18; A. 19; C. 19, &c.; P. 18; V. 8.
Length 3 inches.

“Caught at night, off Cape Ines, Tierra del Fuego, two miles from the shore, in thirteen fathoms.”—D.—The specimen is probably not full-sized,