CHAPTER III.
DESCRIPTION OF PLATES.
Amongst the best known shells in any part of the world the Nautilus takes a leading position. Named Argonauta by scientific men, after the Argonautae, or sailors of the Argo, it has been the subject of many legends from the earliest times. Aristotle describes it as floating on the surface of the sea in fine weather, and holding out its sail-shaped arms to the breeze. This is now known to be incorrect, as the use it makes of these arms is to help it in swimming through the water. New Zealand's specimen, the Argonauta nodosa, also known as Argonauta argo, the most beautiful of the four known species, is depicted on Plate I. Being a floating shell, and found even hundreds of miles from land, our Nautilus is not peculiar to New Zealand. Its beautiful white, horny-looking shell can be obtained from most parts of the Pacific and Indian Oceans, but in no part of the world can finer specimens than ours be found. It is known to the Maoris as Muheke or Ngu, and colloquially as the Paper Nautilus.
The animal that produces this shell belongs to the octopus, or cuttlefish, family. The male is an insignificant-looking octopus, about an inch long. The female grows many times larger, as can be imagined from a glance at the shell in the plate, which measured nine inches across, and was found at Mayor Island, in the Bay of Plenty, and is now in the possession of Mr. C. Spencer.
In the shell the female lays her eggs, and in it the young are hatched. Unlike all other shells, the Nautilus is not moulded on the animal, nor is she even attached to her shell by muscles. When washed ashore she can wriggle out of her shell and swim away. In her shell she lies as in a boat, propelling herself by slowly sucking up water, and violently ejecting it through a funnel, or syphon, at the same time using her arms as oars, to increase her speed. Dame Nautilus can sink to the bottom of the sea if she chooses; and when wishing to crawl about the sand or rocks she turns over and carries her shell on her back, like a snail.
Beside the Nautilus is her little cousin, the Spirula peroni, which sometimes, although not quite scientifically correct, is called an Ammonite. Our Nautilus is frequently found alive, but only one living specimen of this Ammonite has hitherto been caught, though several shells have been obtained from different parts of the world with portions of the fish attached.
Neither towing nets nor dredges have been successful in catching the Ammonite, so it evidently does not live either on the surface or bottom of the sea, but probably between the two, in deep water. The shell is in a number of divisions, connected by a fine tube, and no doubt its use is to regulate the depth at which the animal wishes to stay. This the creature does by filling a number of the divisions with water or air, according as it wishes to sink deeper or float upwards. After a gale, on looking amongst the wrack cast up by the highest waves, large numbers of our Spirula will be found. Light and fragile the shells are, and they ride ashore without injury, and frequently are found covered with small barnacles, a proof that many weeks must have elapsed between the death of the owner and the casting ashore of its shell. In places in New Zealand, and elsewhere, large fossil deposits of Spirula peroni occur. It is worth remembering that, even though this shell is found as far away as England, the only living specimen was caught on the New Zealand coast. Our only other floating shells are three species of Janthina, or violet shells, two of which are shown on Plate VII., Figures 1 and 2.
The first three shells on Plate II. belong to the Murex family. From this species the ancient Tyrians obtained a portion of their celebrated purple dye. The Janthina family (Plate VII.), however, contributed the greater portion. The dye was extracted by bruising the smaller shells in mortars.