The shell, in this way, acquired no little buoyancy, and probably stood up like a church spire, the animal keeping close to the bottom to lie in wait for any hapless mollusc or trilobite that might chance to come in its way. The _nautilus_ (Fig. 27), which still lives in our seas, occurred likewise in those of the Carboniferous period. It was a coiled shell; in truth, just an orthoceras rolled up in one plane like a coil of watch-spring. An allied form, called the _goniatite_ (Fig. 27), had the margins of its septa of a zig-zag form, like the angles of the wall round a fortified town. When the thin outer coating of the shell is removed, the ends of these partition-walls are seen to form strongly-marked angulated sutures or joints, where they come in contact with the shell. Hence the name of the genus--_angled_ shell. All these animals were predaceous. They did not confine themselves to the lower forms of life, polyps and medusæ, nor even to the humbler tribes of their own sub-kingdom, but hesitated not to wage war with creatures greatly higher in the scale of creation than themselves, such as the smaller fishes. They swarmed in the palæozoic seas, and well merited the title of scavengers of the deep, that has been bestowed on the sharks of our own day. They seem to have performed a function now divided partly among the fishes and partly among the higher gastropodous molluscs. And accordingly we find that as these latter tribes increased, the orthoceratites, and goniatites, and ammonites waned. At the present day, of all the palæozoic cephalopods there remains but one--the nautilus[40]; a and so rare is it, that up to the year 1832, all sorts of fanciful notions existed as to its nature and functions. In fact, the nautilus was a sort of myth which any naturalist could dress up as he chose, much as the old poets used to picture the ship Argo. A specimen was at length procured and intrusted to the examination of Professor Owen, by whom its anatomy was studied, and afterwards philosophically described in an elaborate monograph. Then, for the first time, did geologists obtain a true notion of the nature of those siphonated shells, which lie grouped by hundreds in the palæozoic and secondary formations. Yet we still want an account of the habits of the nautilus. The older naturalists alleged that it could at pleasure rise to the surface or sink into the depths of the ocean; that it could spread out its fleshy arms and float across the waves or draw them in, capsize the little vessel, and so return to a creeping posture among the sea-weed at the bottom. These statements may to some extent be true, for the chambers of the nautilus shell must impart great buoyancy to it. But in the meantime the story of the sailing propensities of the animal is derived from a sort of mythic age, and must be viewed with some little suspicion. Until further observations are made, we shall neither fully understand the economy of the nautilus