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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 heen 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.
MUREX ZELANDICUS (Plate II.).— Fig. 1 is known as the spider shell, from the spines, which look like spider’s legs. It is a white or greyish shell, about two inches in length. The long spines would interfere with the growth of this Murex if it had not the power of dissolving them as the outside of one whorl becomes the inside of the next. The removal is supposed to be assisted by chemical action, as the saliva of some shellfish is known
