Art. VII.—Description of a new Species of Paper Nautilus (Argonauta gracilis).

Transactions and Proceedings of the Royal Society of New Zealand, Volume 17, 1884, Page 58

Art. VII.—Description of a new Species of Paper Nautilus (Argonauta gracilis). By T. W. Kirk. [Head before the Wellington Philosophical Society, 9th July, 1884.] Plate XIII That we have in New Zealand two species of the beautiful “Paper Nautilus,” so called on account of the extreme delicacy of its shell, I have for some years felt sure; but although I have examined numerous specimens, I have not until lately been able to obtain a sufficiently good series of each form to justify the creation of a new species, and am now indebted to Mr. C. H. Robson of Te Mahia, who had himself noticed the difference, for the loan of several examples which supply the links required to render the evidence complete. The larger series examined, the individuals of which range from 1 ¼—9 inches across, undoubtedly belong to A. tuberculata, Shaw. The description given is defective, yet a comparison of the shell with drawings by Chenu, Reeve, and other authors, is conclusive. I propose to amend the description as follows:—“Shell compressed, sides with transverse plications which are longitudinally tuberculiferous.” Aperture nearly square posteriorly, margin much thickened, and the angles produced outwards so as to form pointed wing-like processes, projecting beyond the sides of the shell. Keels two, with compressed tubercles, white, brown on the spire, where also the keel tubercles are blackish-brown. What I now consider to be a new species is distinguishable from the foregoing at a glance. The whole shell has a more graceful and regular outline, and is much more fragile looking, the aperture is narrower and rounded, especially posteriorly, there is no sign whatever of wing-like expansions, indeed the sides have a graceful sweep where the angle occurs

Arconauta Cracilis, n.sp. Arconauta Tuberculata, Shaw.

n A. tuberculata. The transverse processes are finer and more numerous, consequently the tubercles forming the keels are smaller, the space between the keels is much less. Some of these differences have been noticed before, but were thought to be probably due to age; that such is not the case will be apparent to all who examine the specimens on the table. A shell containing the animal having been sent to the Canterbury Museum by Mr. Robson, Dr. von. Haast very kindly granted the loan of them, and at once forwarded them for my examination. The animal proves to belong to the same species as a specimen from the Chatham Islands, described by Professor Hutton on p. 2 of the Catalogue of Marine Mollusca (1873), under the name of A. tuberculata. The specimen now under consideration was procured at Portland Island, is somewhat larger than the Chatham Island one, and shows some slight differences, but only such as are frequently found between members of the same species. Such being the case, I cannot do better than quote Professor Hutton's description. “Animal.—Body oblong, rounded behind, smooth, spotted with violet: eyes large, prominent; siphuncle united to the base of the arms by a lateral membrane; arms tapering, except the dorsal pair, which are palmate at the end, these are the shortest, the next pair to them the longest, and the others graduated; the lowest pair are keeled on the outside; membrane small, all the arms equally webbed; cups large, less than their own diameter apart, in two rows, with a single row of rather small cups round the mouth.” To which he adds the following remark:—“As the shell of this animal was not obtained, I refer it doubtfully to this species, as it differs from Dr. Gray's description.” It is satisfactory that conclusive evidence is now forthcoming, and that this animal with its exquisitely beautiful shell is to enjoy specific distinction. I would therefore suggest for this latest addition to the fleet, the name of Argonauta gracilis.