Art. XIX.—On a Torpedo (T. fusca,? n. sp.) recently caught near Dunedin.
[Read before the Otago Institute, 7th May, 1883.]
The specimen upon which the following description is founded was caught at Purakanui, Otago, towards the end of last year. As far as I know it is only the second example of the genus which has been recorded in New Zealand,* the other having been caught at Napier, in 1868, by Captain Fairchild, and named by Professor Hutton† Torpedo fairchildi.
The present specimen agrees in most respects with T. hebetans,‡ of which I should be disposed to consider it a variety, but for the fact that it differs from that species in at least one character considered by Günther to be of specific importance. I therefore propose to name it provisionally T. fusca.
The species of Torpedo are divided by Günther into two groups, containing respectively those with fringed and those with unfringed spiracles. My specimen belongs to the latter subdivision, in which only two species, T. hebetans, and T. narce, are included in the “Catalogue of Fishes.” A query is, however, placed against T. emarginata of McCoy,¶ indicating that its position as a synonym of T. hebetans is doubtful. Hutton's T. fairchildi has also unfringed spiracles, and it is apparently the only new species of Torpedo which has been recorded since the publication of the “Catalogue of Fishes.”
[Footnote] * Since this paper was written, two specimens of Torpedo have been caught in Napier Harbour, but the description of them (N.Z. Journ. of Sci., July, 1883) is not sufficiently exact to allow of their identification.
[Footnote] † Hutton and Hector, Catalogue of N.Z. Fishes, 1872.
[Footnote] ‡ Günther, Catalogue of Fishes, viii., p. 449.
[Footnote] ¶ Ann. and Mag. Nat. Hist., 1841.
There are thus three species and a doubtful fourth with unfringed spiracles: from these the Purakanui specimen differs in the following characters:—
From T. hebetans:
From T. narce:
From T. emarginata:
From T. fairchildi:
According to Günther, the most important of these characters are those relating to the dorsal fins, namely, the position of the first dorsal with regard to the pelvic fins,* and the relative size of the two dorsals. For instance, in T. hebetans, “the first dorsal fin is twice as large as the second, and situated nearly entirely behind the root of the ventrals,” while, in T. narce, “the first dorsal fin is not twice as large as the second, and only its anterior half is opposite to the base of the ventrals.”†
[Footnote] * Dr. Günther would earn the gratitude of morphologists if he would give the weight of his authority to a much-needed change in the nomenclature of fins. Every one knows that the fins of fishes are divisible into median and paired; the former being either dorsal, ventral, or caudal; the latter pectoral or pelvic. If, then, the name “anal” could be abolished, the so-called anal fins being called ventrals, and the so-called ventrals pelvics, a very great improvement would be effected: the authority of such a book as the “Catalogue of Fishes” could not fail to effect the change of names within a reasonable period.
[Footnote] † Günther, l.c.
Similarly in T. fairchildi, the first dorsal is said by Hutton to be “over the ventrals, with the posterior edges of both in a line,” and to be “about one and a half times the size of the second.”
Unfortunately it is not stated by either Günther or Hutton whether by “size” is meant area, or greatest length, or vertical height, or length of base; nor whether, in giving the position of the first dorsal with regard to the ventrals, its base or line of attachment should, as one would naturally think, be made the standard. A reference to fig. 3 (pl. xxii.) will show the necessity of a strict definition of terms, in a case where such apparently insignificant differences are considered as of specific importance. The figure shows the two dorsals of T. fusca of the natural size, and it will be seen that while the line of attachment (a b), and the vertical height (c d), of the first dorsal are almost exactly twice the corresponding dimensions (a' b′, c′ d′) of the second, yet the greatest length (a c) of the first is considerably less than twice that of the second (a′ c′), the proportions of the two being, in fact, as 13 to 8. The figure also shows that the actual posterior boundary of the first dorsal (c) projects considerably beyond the posterior end of the base (b), and that it is therefore important to state which of the distances a b and a d is to be taken in considering the position of the fin with regard to the ventrals.
It is rather strange that the peculiarity of the caudal fin of Torpedo is not mentioned in the “Catalogue of Fishes”: it is certainly worthy of notice that, although belonging to an order in which heterocercality is the general rule, Torpedo has a tail-fin which is diphycercal, at the same time simulating in a remarkable way the homocercal tail of a Teleost.
The characters of the specimen described are as follows:—
Torpedo fusca,? n. sp.
Pl. xxii., fig. 1.
Spiracles not fringed, their distance from the eyes little more than their own diameter. The greatest length of the first dorsal fin (fig. 3) is to that of the second as 13 is to 8: the base and the vertical height of the first dorsal are almost exactly twice those of the second. The posterior end of the base of the pelvic fin is nearly opposite the middle of that of the first dorsal. No distinct longitudinal pit at the angle of the mouth, but several irregular folds (fig. 2). The length of the band of mandibular teeth has the same proportion to the gape as in T. narce. Dark brown above, mottled with irregular lighter patches: greyish-brown beneath.
|Total length||26.0 inch.|
|Length of disc||16.5 "|
|Breadth of disc||14.0 "|
|Length of electric organ||7.5 "|
|Average breadth of organ||2.5 "|
There are about 70 columns to the square inch in the anterior, about 40 in the posterior part of the electric organ.
|Fig. 1.||Torpedo fusca, from above (1/3 nat. size).|
|Fig. 2.||" " The mouth and adjacent parts (½ nat. size); f.n.p., fronto-nasal process; na, nostril; pt. qu, upper jaw; mck, lower jaw.|
|Fig. 3.||" " The dorsal fins (½ nat. size); ab, base of 1st and a'b′ of 2nd dorsal; ac, greatest length of 1st and a'c′ of 2nd; cd, vertical height of 1st and c'd′ of 2nd.|