FAMILY: ESOCIDAE

EXOCOETUS EXSILIENS. Bl.?

Exoctus 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 the 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 striś on the surface of the basal portion; in others these striś converge to form a small but very regular fan; and the scales appear to vary a good deal on different parts of the body.

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 to 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 its 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, etc.; 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. 18į S. It appears to be the E. exsiliens of Bloch, but as I am not aware that the species of Exocoetus have been ever rigorously 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.2

2 Swainson is of opinion that Ďmore than double the number of species of Exoctus really exist above those that have been describedí. Nat. Hist. of Fishes, vol. i, p. 299.

 

FAMILY: SALMONIDAE

1. TETRAGONOPTERUS ABRAMIS. Jen.

PLATE XXIII. FIG. 1

T. corpore subrhomboideo, compressissimo, altitudine fere dimidium longitudinis, pinn‚ caudali exclus‚, aequante: osse maxillari angusto, retrorsum arcuato: pinn‚ dorsali triangulari, suprŗ ventrales accuratŤ exorienti; anali laevi, long‚, altitudine retrÚ cito decrescente; utr‚que plicis membranaceis, radiis longitudinaliter adhaerentibus, instruct‚: squamis in line‚ laterali 46, in line‚ inter pinnas ventrales et dorsalem transvers‚ 17

B. 4; D. 1/10; A. 2/30; C. 19, etc.; 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 projectingconsiderably. 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 striś, and with two coloured deeper striś on the free portion diverging from the centre in a V-like form: some scales have three or four of these coloured striś, 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 sort 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 axillae of the ventrals is an elongated scale, not half their length.

Colour. ĎBack 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.í - 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.3 It differs from the T. chalceus of Spix , in its much smaller scales, not to mention other points of dissimilarity.

3 Thesaurus, vol. iii, pl. 34, f. 3.



 

2. TETRAGONOPTERUS RUTILUS. Jen.

PLATE XXIII. FIG. 2

T. corpore ovali, compressissimo, altitudine tertiam partem longitudinis, h‚c ad basin furcae caudalis mens‚, aequante: osse maxillari angusto, retrorsum arcuato: pinn‚ dorsali subtriangulari, paululum pone ventrales exorienti; anali laevi, long‚, altitudine retrÚ cito decrescente; utr‚que plicis membranaceis, radiis longitudinaliter adhaerentibus, instruct‚: squamis in line‚ laterali 40, in line‚ inter pinnas ventrales et dorsalem transvers‚ 14

D. 1/9; A. 2/27; C. 19, etc.; 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. ĎBack 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.í - 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 longituidinis, caudali exclus‚, aequante: osse maxillari paulo dilatato, recto: pinn‚ dorsali suboblong‚, alt‚, pone ventrales exorienti; anali scabr‚, altitudine retrÚ gradatim decrescente; radiis plicis membranaceis nullis: squamis in line‚ laterali circiter 38, in line‚ inter pinnas ventrales et dorsalem transvers‚ 12

D. 1/9; A. 3/22; C. 19, etc.; P. 13; V. 8

Long. unc. 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 striś 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 distinguished 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 TAENIATUS. Jen.

T. corpore ovali, valde compresso, altitudine tertiam partem longitudinis, h‚c ad basin furcae caudalis mens‚, aequante: osse maxillari margine posteriore recto: pinn‚ dorsali suprŗ ventrales accuratŤ exorienti; anali laevi, altitudine retrÚ cito decrescente; radiis plicis membranaceis nullis: squamis in line‚ laterali 40, in line‚ inter pinnas ventrales et dorsalem transvers‚ 14

D. 1/10; A. 3/22, etc.

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 aequante: ore parvo; osse maxillari brevissimo, dilatato, margine posteriore recto: dentibus minutis, multicuspidatis: dorsali subtriangulari, pone ventrales exorienti; anali (in uno sexu?) scabr‚, altitudine retrÚ subito decrescente; his pinnis plicis membranaceis nullis: squamis in line‚ longitudinali 35, in line‚ inter pinnas ventrales et dorsalem tranvers‚ 10: line‚ laterali interrupt‚, haud finem pinnś pectoralis attingente

D. 1/10; A. 2/18; C. 18, etc.; 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 curing 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 striś on the basal portion, and consequently no fan; but they are very regularly marked with the usual finer striś 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.
Hydrocyon 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 striś, but no deeper-cut striś 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 of 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 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, etc.; P. 12; V. 8

Length 4 inches 3 lines

Colour. ĎBluish silvery.í - 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 4 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.

4 Voy. dans L'Amer. Mťrid., Atl. Ichth., pl. 9, fig. 2.

 

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, haec subaequantibus, retroductis. Dentes minuti, acuti, in maxill‚ utr‚que uniseriati, in lingu‚ et vomere longitudinaliter biseriati, in ossibus palatinis nulli. Apertura branchialis amplissima, membran‚ triradiat‚, subtus profundŤ emarginat‚. Pinnae, 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 Cyprinidae 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 Salmonidae, 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 .5 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 Siluridae , 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 Cyprinidae, and of the usual form; the subopercle also is very distinct;6 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 Siluridae in having no coecal appendages, though the air-bladder is similar to that of the ordinary Salmonidae. 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.

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

5

6 Valenciennes says, in his preface to the fifteenth volume of the Histoire des Poissons, that none of the Siluridae have the subopercle; and that the absence of this bone serves to distinguish them from Cobitis .

 

1. APLOCHITON ZEBRA. Jen.

PLATE XXIV. FIG. 1

A. obscurŤ plumbeus; fasciis nigris transversis: maxillis aequalibus

B. 3: D. 11; A. 2/14; C. 16, etc.; P. 18; V. 7

Long. unc. 9. lin. 6

Form. General form somewhat resembling that of the Mackerel 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. Moth 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 45į 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 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 rays simple, the others branched. Caudal forked for half its length, the lobe 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 axillae.

Colour. ĎDull leaden colour.í - 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 of 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 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 sophageal portion with prominent longitudinal plicś. Its contents, so far as they could be ascertained, consisted of the remains of caddis-worms. The intestine was large, without any ccal 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 Salmonidae . 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 TAENIATUS. Jen.

PLATE XXIV. FIG. 2

A. olivaceus, punctis fuscis minutissimis irroratus; lateribus vitt‚ longitudinali argente‚: maxill‚ inferiore longiore

B. 3; D. 12; A. 2/13; C. 16, etc.; 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.