Part 21

Psenes leucurus, Cuv. et Val.? Hist. des Poiss. tom. ix. p. 197.

Mr. Darwin’s collection contains two individuals of a species of Psenes, in reference to which his notes state that they were taken in Lat. 17° 12′ S., Long. 36° 33′ W., a hundred and twenty miles from the nearest land above water, though shoals were considerably nearer. They do not measure more than one inch eight lines in length; and from their small size, and their not being in a very firm state of preservation, it is hardly possible to say whether they are new or not. In form, they differ but little from the P. cyanophrys of Cuvier and Valenciennes: still they are evidently not that species, and one point of difference consists in the lateral line, which terminates beneath the end of the second dorsal, and is not carried on to the caudal, as represented in the figure of the above species in the “Histoire des Poissons:” the eye too appears rather larger; the forehead is hardly so much elevated, and the pectorals are shorter than the head. Perhaps it may be the P. leucurus of the above authors; though this species is from the Indian seas, so that its range must be considerable if the same. The description of the P. leucurus in the “Histoire des Poissons” is too short to determine this point. It is said to have been so named on account of its whitish tail, all the other fins being black. In the present species, the fins are likewise black, or at least dusky, except the caudal, which Mr. Darwin’s notes, taken from the recent fish, state to have had “a pink tinge.” In the same notes it is added,—“belly silvery white mottled with brownish black; sides bluish with dusky greenish markings; iris yellow, with dark blue pupil.” The fin-ray formula is as follows:

D. 10—1/27; A. 3/27; C. 17, &c.; P. 17 or 18; V. 1/5.

Though these specimens are small, they have the appearance of being nearly full-sized. Cuvier and Valenciennes state that their specimens of the P. leucurus do not exceed two inches in length.

STROMATEUS MACULATUS. Cuv. et Val.?

Stromateus maculatus, Cuv. et Val. Hist. des Poiss. tom. ix. p. 296.

FORM.—General form so extremely similar to that of the S. Fiatola of the Mediterranean as to preclude the necessity of a detailed description. Greatest depth one-third of the length: head one-fifth of the same. Number of rays in the dorsal and anal fins somewhat greater than in the S. Fiatola. The height of the dorsal also a little greater, being contained about three times and a half in the depth: the fifth and sixth soft rays longest. Fleshy part of the tail more slender. Pectorals about the length of the head.

B. 6; D. 7/41; A. 5/40; C. 17, besides several short; P.23; V. 0. Length 8 inches 6 lines.

COLOUR.—“Silvery blue above, with regular circular leaden spots.”—D. The spots are small, and of nearly equal size: they prevail from the back downwards to about the middle of the depth, and advance a little on the base of the dorsal fin. The arrangement of them is much as described in the “Histoire des Poissons.”

Habitat, Chiloe, West Coast of S. America.

It is just possible that this may not be specifically the same as the S. maculatus of Cuvier and Valenciennes, but it comes so extremely near that species that I do not feel authorised in describing it as distinct without seeing more specimens. It is stated by the authors above mentioned, that the fin-ray formula of the S. maculatus is the same as that of the S. Fiatola: in the specimen here described, the number of rays in the dorsal and anal fins appear to me somewhat greater; but as the spines of these fins are very minute at their commencement, and not readily counted, nor very distinguishable from the soft rays, perhaps the discrepancy may arise from a difference in the mode of computation. What is more to be noted is, that the spots, although they agree in form and mode of arrangement, are said by Mr. Darwin, in his notes taken from the recent fish, to have been “leaden;” whereas it is stated in the “Histoire des Poissons” that they are “yellow.” Perhaps they may vary in colour according to the period of the year. There is likewise a difference in locality as regards latitude. The S. maculatus is said to be common in the market at Lima, and to have been brought also, both by M. D’Orbigny and M. Gay, from Valparaiso. Mr. Darwin’s specimen, however, was taken as far south on the western coast of S. America as Chiloe.

Mr. Darwin’s collection contains another specimen, either of the same species as that described above, or one so extremely similar to it as not to be distinguishable in the case of this specimen, which is in too bad preservation to admit of an accurate description of it being given. The following, however, are Mr. Darwin’s notes taken from the recent fish:—

COLOUR.—“Whole body silvery; upper part of the back iridescent blue, lower greenish; spotted with coppery-lead circular patches.”—D.

This specimen measures ten inches and a half in length. It will be observed that the colour of the spots is still said to have been “lead,” though inclining to coppery. It was not taken at the same place as the other, but at Port St. Julian, in central Patagonia; if therefore they are both referable to the S. maculatus, this species will have been proved to have a wide range in point of latitude, and also to occur on both sides of the S. American Continent, which is remarkable, considering that it is found so high up the western side as Lima.

FAMILY.—TEUTHYDIDÆ.

1. ACANTHURUS TRIOSTEGUS. Bl. Schn.

Acanthurus triostegus, Cuv. et Val. Hist. des Poiss. tom. x. p. 144. —— Hirudo, Benn. Fish of Ceyl. pl. xi.

This species, which appears to be well known, and to have been described by several authors, was found by Mr. Darwin on coral reefs at the Keeling Islands. Cuvier and Valenciennes observe that it has a wide range through the Indian and Pacific Oceans. Mr. Darwin’s specimen agrees in every respect with the description in the “Histoire des Poissons,” except in having one ray more in the anal fin: its length is not quite five inches.

2. ACANTHURUS HUMERALIS. Cuv. et Val.

Acanthurus humeralis, Cuv. et Val. Hist. des Poiss. tom. x. p. 170.

FORM.—General form oblong-oval. Greatest depth just behind the insertions of the pectorals; contained exactly twice in the length of the oval of the body (measuring this last from the end of the snout to the base of the caudal spine), and three times in the entire length (measuring this last to the extremities of the lobes of the caudal fin.) Profile convex before the eyes, whence it descends nearly vertically to the mouth. Height of the head a little exceeding its own length. Eyes very high in the cheeks, and in front of each a grooved line passing horizontally forwards towards the nostrils; which last consist of two small round orifices, the anterior one larger than the other, and partially covered by a membranous flap. There are seventeen teeth in the upper jaw, and sixteen in the lower: those above have the cutting edges crenated, and likewise the lateral edges for nearly half-way down; this most observable in the middle ones, in which the crenations amount to eight or ten in number: those below similar, but with the crenations not quite so numerous, and in some of the teeth at the sides of the jaw almost confined to the cutting edges. Scales minute; those taken from the middle of the body appear of an oblong form, their apical portions dotted, and ciliated with from twelve to eighteen very minute denticles, their surface marked with extremely fine delicate striæ, not distinguishable without a strong lens.

The lateral line follows the curvature of the back; at about one-fifth of the depth. The spine on the sides of the tail is strong, and sharp-pointed, and very slightly bent. No reclined spine before the dorsal. Both the fin just mentioned and the anal have their soft portions terminating posteriorly in rather an acute angle: also both have a scaly membrane at the base, and rows of minute scales between the soft rays extending for about one-third or more of their length. The first ray of the anal is very minute, and so much concealed in the skin as to be easily overlooked. The filaments of the caudal are sharp-pointed, and extend as far again as the middle rays: the upper one rather longer than the other. The pectorals are contained three times in the length of the oval of the body. Ventrals attached a little further back, sharp-pointed, and terminating in the same vertical line with the pectorals, both being laid back.

D. 9/23; A. 3/23; C. 16, &c.; P. 16; V. 1/5. Length, to the end of the caudal lobes, 7 inches.

COLOUR.—The colours appear to have been exactly as described in the “Histoire des Poissons.” Mr. Darwin’s notes taken from the recent fish state, “splendid verditer blue and green;” but do not enter into the details of the markings.

Habitat, Tahiti.

Obtained at Tahiti, where it had been previously found by MM. Lesson and Garnot. Mr. Darwin’s specimen accords with the characters given by Cuvier and Valenciennes, except in having two soft rays less in the dorsal, and one less in the anal. Their description, however, is not very detailed.

FAMILY.—ATHERINIDÆ.

1. ATHERINA ARGENTINENSIS. Cuv. et Val.?