A guide to the fossil invertebrate animals in the Department of geology and palaeontology in the British museum (Natural history) ... / With 7 plates and 96 textfigures.

British Museum (Natural History). Department of Geology

Date:: 1911

Credit: A guide to the fossil invertebrate animals in the Department of geology and palaeontology in the British museum (Natural history) ... / With 7 plates and 96 textfigures. Source: Wellcome Collection.

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$Gallery of Huleoatcphaims'(voiw Wm IVn llaiidiaii near Moscow, sliowiiig W^/case ividesceiit shell, 'i'he large Holcodciihanui^ iind the 0_ still larger rerisphinrtes (/if/anfctin, from the I’ortlaiul Stone of England are in the AVall-case. A small si)ecimen of the latter species had the shell turned into silica, and the inlilling limestone has been dissolved out, exposing the shape of the septa and the position of the siphuncle. Wall-case The Lower Cretaceous rocks have not furnished many ammonites, but the large ramlioplileH Dcslwycsi from the Lower Greensand carries on the general plan of the genera just mentioned. Other new genera appear in the series from Table-oases the Albian of Kscragnolles (Var), and i'rom the coaeval Gault 10,11, &12. p’olkestone. The iridescent appearance of these and other ammonites ])reviously noticed is due to the solution of the outer layers of the shell, by which the inner nacreous layers are ex])osed. Here we meet with Hoplites, characterised by a broad groove on the outer margin of its shell, similar to that previously seen in the otherwise unlike Hchlolhcimia of the Lower Lias and ParJdnsojiia of the Lower ( )olites. The specimens of this genus from Folkestone form a series illustrating the decline of ornament from tuberculate, through ribbed, to smooth. Similarly Mortoniccras shows a decline from highly tuberculate to ribbed. ]\[. rostratam marks Wall-ease a wide-spread horizon in the All)ian, and there is a splemlid .series of it from both Gault and Upper Greensand, preserving the long rostrum at the .shell-aperture. rhijUoccras Guettardi and several species of Jfolcodisrii.s show periodical constric- Table-case tions of the shell-aperture. The specimens from the Cam- bridge Greensand are derived from the underlying (Jault, and those from the Led Chalk seen in the next ca.se are also of that age. Table-cases The Cenomanian forms in the Table-case include 12 & 13. characteristic Mctacanthoplites roloinagcnsis from llouen, Brahmaites from Pondicherry, and Fachydiscus from various European localities. The Upper Cretaceous rocks ol South Dakota yield specimens of Flacenticeras with elaborate sutures. Tissoiia, on the other hand, from the Senouian of jVlgeria, shows that return to a Ceratite form of suture which is found in many late Cretaceous ammonites. Among the British specimens from the Chalk Marl and Chalk are many iigured in 1). Sharpe’s monograph published by the Palaeonto- graphical Society. Those from the Chalk Marl include a tine series of Schloeiibachia ranging from the tuberculate Schlocnhachia Oonpei, through the more or less rilibed$