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The three plates characteristic of Aptychopsis have been described as a jaw apparatus in this orthocone cephalopod as well as an operculum for it. Due to the limited material, interpretations have in various cases been made from photographic illustrations and those results are discussed in this article. The area of the aptychopsid plates is compared with the apertural area of the cephalopod and the results show a great similarity. Arguments for and against soft parts outside the aptychopsid plates are discussed as well as the position of the plates. Material from a Silurian shale in southern Sweden is described. ? Aptychopsis, aptychopsid plates. Cephalopoda, operculum, jaw apparatus, Silurian.