OCR Text |
Show 126 ZOOLOGY OF TilE VOYAGE OF THE BEAGLE. FoRM -Sh·l l more oval an d e1 o nga t e d than the last species' the profile falling in a gentle. curve from t·h e dorsal to the en d of t h e snou t · Depth exactly one-third of the length, excludmg caudal: head one-fifit l1 of the en t.t re 1e n gth, caudal included. Maxillary rather. dilated towards the bot-tom, an d qm' te st rat· gh t, not curving backwards as in both the last. speCles. Teeth rather larg.e r, an d more conspt·c uous. Nostrils larger· Only twelve sc.a les m. th. e depth, the .l ateral lme occupy·m g t h e seven th row firom the top·· thirty-seven or thirty-eight m the l.a teral hne. Scales of a rath er dm·~c ren t 1i.•' orm ·, the basal margin more sinuous, the free margm not• so reg• ularly curved, the coloured strire hardly obvious. Dorsal more oblong than :riangul~, h1gher m .rela- t.w n to t b e d ep th , of wh'tch it equals two-thirds' commencing at a pomt anteriOr to the .m tdille 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 ~ore nearly equal, the posterior part of the fin not being so much sloped off: there are three spmes at t~e commencement, the first two minute, the third not quite half the length of the so~t rays : t~lS fin is furthermore distinguished from that of the two former species by the rays bemg. 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 e1ther of the two last species: the back and upper part of the sides being brownish. . A humeral ~usky spot, a~d the remains of what was probably a bright silver band along the m1ddle of the s~de fro~ the g1ll to the caudal. At the base of the caudal is a dusky spot, which is prolonged m a hne 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 TJENIATUS. Jen. T. corpore ovali, valde compresso, altitudine tertiam pm·tem longitudinis, ltdc ad basin jw"Cre caudalis mensd, cequante: osse maxillari margine poster·iore r·ecto : pinna dorsali supra . t•entt·ales accttt·ate exorienti ,· anali lcevi, altitudine 1·et1'f) cito decrescente; mdiis plicis membmnaceis nul/is : squamis in linea laterali 40, in lined inter pinnas ventmles et dorsalem tmnsversd 14. D. 1/1 0 ; A. 3J22, &c. LoNG. unc. 2. lin. 2. l'om.r.-Dcpth and general form similar to fhose 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-nam~d species, being of nearly equal breadth throughout. The teeth are more numerous than 10 either, amounting in the lower jaw to fourteen or more. The vcntrals are in an exact line with the commencement of the dorsal. FISH. 127 CoLoun.-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. TETRACS.ONOPTERUS INTERRUPTUS. Jen. PLATE XXIII. fig. 4. T. corpore ovali, valde compresso: altitudine tertiam partem longitudinis totius cequante: ore parvo ,· osse muxillari brevissimo, dilatato, margine posteriore recto: dentibus minutis, multicuspidatis: dorsali subtriangulari, pone vcntrales exorientt; anali (in uno sexu ?) scabrd, altitudine 1·etro sub ito decrescente; !tis pinnis plir:is membranaceis nullis : squamis in lined longitudinali 35, in linea irder pinnas ventmles et dm·salem tmnsversd 10 : lined laterali interrupt&, ltaud .finem pinnce pectoralis attingente. D. 1Jl0; A. 2/18; C. 18, &c; P. 11; V. 7 LoNG. unc. 2. lin. 8. Fon11r.-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 portiou of the gill-flap. Scales relatively larger; only ten in the depth, and thirty-five in the length. They have no deep strire on ilie basal portion, and consequently no fan; but they are very regularly marked with the usual finer strire 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 |