. A conchological manual. Shells. 16 INTRODUCTION. Septa. The septa are simple in some species^ as in the Nautilus,, fig. 13. In others they are undulated^ having waved edges, as in some species of Ammonites; in others they are angulated, as in Goniatites, fig. 480 in the plates; and in the greater number of instances, among the Ammonites, they are arbores- cent, or 13. Section of Nautilus.—14. Uudulating Septa.—15. Arborescent Septa. In the above section of a Nautilus, fig. 13, diminished in size, shewing the whorls and chambers (c), it will be seen that the edges of the septa (s)
. A conchological manual. Shells. 16 INTRODUCTION. Septa. The septa are simple in some species^ as in the Nautilus,, fig. 13. In others they are undulated^ having waved edges, as in some species of Ammonites; in others they are angulated, as in Goniatites, fig. 480 in the plates; and in the greater number of instances, among the Ammonites, they are arbores- cent, or 13. Section of Nautilus.—14. Uudulating Septa.—15. Arborescent Septa. In the above section of a Nautilus, fig. 13, diminished in size, shewing the whorls and chambers (c), it will be seen that the edges of the septa (s) are formed in one simple curve. In fig. 14, the upper part of an Ammonite, the undulating line will be seen; and in fig. 15 a specimen is given of the arbo- rescent septa. Siphon. The Siphon is dorsal when placed near the outside of the whorls; central when near the middle; and ventral when near the inside of the whorl, or that part which leans against the last volution. When it passes uninterruptedly from one chamber to another, it is described as continuous, as in the case of Spirula; when, on the other hand, it only passes through the septum a little distance, and opens into the chamber, as in Nautilus, it is Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Sowerby, G. B. (George Brettingham), 1812-1884. London H. G. Bohn
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