Fig. 16. A polished section of a Nautilus (_N. truncatus_, of Sowerby), from the Inferior Oolite of Yeovil, Somersetshire. The chambers are filled up with crystalline limestone, with the exception of the six outermost cells, in which are left hollows that are lined with calcareous spar. Fig. 17. Polished section of an Orthoceratite, from the Silurian strata of Oëland, Sweden. Fig. 18. The discoidal part of a Lituite from the same locality as fig. 17. Fig. 19. A polished slab of grey marble, from the Devonian formation of the Rhine. The figures are sections of _Orthoceratites_, _a_; and _Lituites_, _b_. [Illustration: Plate LIX.] PLATE LIX. Fossil Cephalopoda, &c. Fig. 1. A fossil shell named Hippurite (_Hippurites bioculatus_, of D'Orbigny), from the south of France. This shell belongs to a family termed _Rudistes_, whose characters are somewhat problematical,--some naturalists referring them to the bivalves, and others to the univalves. The Hippurite is generally of an elongated conical form, and has internally two obtuse longitudinal ridges; the base is sometimes partitioned by transverse septa. Fig. 5, is a longitudinal section of a specimen in which septa are displayed. The aperture is closed by a moveable operculum, or upper valve, as in the specimen fig. 1. The substance of the shell is cellular and very thick, and when fractured, resembles that of the lamelliferous corals. Some kinds attain a large size, and are called "petrified horns" by the inhabitants of the districts in the Pyrenees where they abound. Though Hippurites are abundant in the chalk of the south of France, and in Spain and Portugal, none have been found in England. The _Spherulite_, a nearly allied genus, which has no internal longitudinal ridges, occurs in the chalk of Sussex: it was first discovered near Lewes. (_Spherulites Mortoni_, of Mantell.)[54] [Footnote 54: Medals of Creation, p. 428.] Fig. 2. The siphuncle of a very large Orthoceratite ("related to the genus _Ormoceras_," Mr. Morris), from the Rhine. Figs. 3 & 4, "show the direction in which the siphuncle in Orthoceratites intersects the septa." Fig. 6. Siphuncle of an orthoceratite (related to _Orthoceras duplex_, of Kissinger), from the Silurian strata, Sweden. Fig. 7. An Orthoceratite (_O. pyriforme_, of Sowerby), from the Silurian strata, Dudley. Figs. 8-15. Various kinds of Belemnites.