File:A guide to the fossil invertebrate animals in the Department of geology and palaeontology in the British museum (Natural history) (1907) (14592795338).jpg

Identifier: guidetofossilinv00brit (find matches)
Title: A guide to the fossil invertebrate animals in the Department of geology and palaeontology in the British museum (Natural history)
Year: 1907 (1900s)
Authors: British Museum (Natural History). Dept. of Geology Bather, Francis Arthur, 1863-
Subjects: Fossils
Publisher: London, Printed by order of the Trustees
Contributing Library: Smithsonian Libraries
Digitizing Sponsor: Biodiversity Heritage Library

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were two types of straight shells,so were there two of coiled shells: one with a protoconch, asmay be seen in models of early goniatites (Fig. 81 n) \ theother without a protoconch, as shown by the model ofNautilus (Fig. 81 a-c). Further examination of the shellsof these two types reveals other differences. The earlycoiled shells with a protoconch are long, narrow, smooth,with septa usually far apart, and with a long deep body-chamber (Fig. 81 n). Those without a protoconch are short,broad, often with a longitudinal ornament, with septarelatively close together, and with a shallow body-chamber(Fig. 81 a). In later forms of these two types otherdifferences appear, such as will be realised by comparingan ammonite (which is one of the former series) with aNautilus (Fig. 82). Generally speaking the siphuncle of anammonite is close to the outside of the coiled shell; theedges of the septa are folded, so that the sutures are compli- 150 GUIDE TO THE FOSSIL INVEETEBEATE ANIMALS. GalleryVII.
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Fig, 81.—The first-formed portions of various chambered Cephalopodshells, a, b, c, Nautilus jpompilius : a, side view; b, front view, theapex broken to show siphuncle passing through septa ; c, apex, showingscar left by protoconch. d, a straight shell of Triassic age, with aplug (p) at its apex, e, a curved Carboniferous nautiloid, Meloceras,with scar (ci). /, g, h, front, side, and upper views of protoconch ofan ammonite, Cosnioceras. i, Protoconch and first chamber of abelemnite. k, Protoconch and five chambers of Bactrites, the shellpartly removed, showing siphuncle. I, m, the first two chambers ofan allied form from which the protoconch has disappeared, leaving acicatrix, shown in m. n, Protoconch and first five chambers ofMwnocej-as cojnpressum, a goniatite. o, Protoconch and part of twochambers of Spirtcla, the shell-wall partly broken away. In g, i, k, o,the siphuncle is denoted by si. c is natural size, the rest greatlyenlarged. (From Foord & Crick. After Barrande, Hyatt

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