Page:Geology and Mineralogy considered with reference to Natural Theology, 1837, volume 1.djvu/279

 Rh siphon. The base of the shell beyond the last plate presents a swelling cavity, wherein the body of the animal seems to have been partly contained.

The Orthoceratites are straight and conical, and bear the same relation to the Nautili which Baculites (see Pl. 44, Fig. 5) bear to Ammonites; the Orthoceratites, with their simple transverse septa, resembling straight Nautili; and the Baculites, with a sinuous septa, having the appearance of straight Ammonites. They vary considerably in external figure, and also in size; some of the largest species exceeding a yard in length, and half a foot in diameter. A single specimen has been known to contain nearly seventy air chambers. The body of the animal which required so large a Hoat to balance it, must have greatly exceeded, in all its proportions, the most gigantic of our recent Cephalopods; and the vast number of Orthoceratites that are occasionally crowded together in a single block of stone, shows how abundantly they must have swarmed in the waters of the early seas. These shells are found in the greatest numbers in blocks of marble, of a dark red colour, from the transition Limestone of Oeland, which some years ago was imported largely to various parts of Europe for architectural purposes.

Together with the Orthoceratite, in the Transition Limestone of Oeland, there occurs a cognate genus of Chambered

the Lias at Lyme, and another species in Alpine Limestone of the Oolitc formation, at Halstadt, in the Tyrol.