The next gallery contains the Cephalopods, a group of Molluscs abounding in extinct species, of which the Belemnites, Turrilites (fig. 55), and Ammonites (fig. 56) are some of the best-known. The form and structure of their nearest living representatives, the various species of Cuttle-fishes, Squids, Argonauts, and Nautilus (fig. 31, page 62) are illustrated by models, drawings, and specimens placed near the entrance of the gallery and along the top-line of the wall-cases. The third gallery contains the remaining Mollusca, with the Brachiopoda, Polyzoa, Echinoderma, Worms, and Crustacea; the fourth, the Corals, Sponges, Protozoa, and Fossil Plants. In these last two galleries most of the British specimens are placed in the table-cases, and those of foreign origin in the cases round the walls. Among numerous other groups which cannot be mentioned, great interest attaches to the Trilobites (fig. 57) of the Palæozoic epoch, which are related to the modern King-Crabs and also have affinity with the Scorpions. Very extensive is the collection of Fossil Plants from the Coal-Measures, among which _Lepidodendron_ and _Sigillaria_, as well as numerous kinds of fern-like leaves, are among the most common. [Illustration: FIG. 54.--UPPER (_A_) AND LOWER (_B_) SURFACES OF PTERICHTHYS, AN ARMOURED DEVONIAN FISH.] [Sidenote: Historical Collections.] The table-cases of the end gallery contain certain special collections of historical interest, either from the circumstances under which they were formed, or the manner in which they came into possession of the Museum, or from their containing a large number of type specimens described and figured in various publications. Hence it has been considered undesirable to break up and disperse these among the general collection. They include the original collection formed by William Smith, the pioneer of geology in this country, the Searles Wood collection of Crag Mollusca, the Edwards collection of Eocene Mollusca, the Davidson collection of Brachiopoda, the types of Sowerby’s “Mineral Conchology,” and lastly, but not least in interest, specimens from the collection of Sir Hans Sloane, which formed part of the nucleus of the British Museum. [Illustration: FIG. 55.--A TURRILITE, FROM THE CHALK.] [Illustration: FIG. 56.--AN AMMONITE, FROM THE OÖLITE.] [Illustration: FIG. 57.--A TRILOBITE, FROM THE LOWER CAMBRIAN OF SHROPSHIRE.] [Sidenote: British Stratigraphical Collection.]