Fig. 8. Construction of the prismatic reduced dorsal shell wall (A–C, F, median, section, growth direction to the left, centrifugal; D, E, transversal section, centrifugal). A. Argonauticeras besairiei Collignon, 1949, BSPG MAo-1772, early Albian, Cretaceous, Ambatolafia, Mahajanga Basin, NW Madagascar; the dorsal shell wall consists of an outer wrinkle layer and a dorsal inner prismatic layer which has two sub-layers; the relief of an injury of the preceding whorl is overgrown by both layers. B. Calliphylloceras sp., BSPG MAn-4512, late Oxfordian, Jurassic, Sakaraha, Morondava Basin, SW Madagascar; the wrinkle layer left imprints in the dorsal inner prismatic layer. C. Desmoceras (Desmoceras) latidorsatum (Michelin, 1838), BSPG MAo-1839, early Albian, Cretaceous, Ambatolafia, Mahajanga Basin, NW Madagascar; the same as in B. D. Cadoceras stupachenkoi Mitta, 1998, BSPG MAn-4790, early Callovian, Jurassic, Makaryev on Unzha River, Russia; the dorsal wrinkle layer is completely replaced by pyrite, i.e., diagenesis. E, F. Aconeceras sp. 1, →