Fig. 18 in The dorsal shell wall structure of Mesozoic ammonoids

Fig. 18. Construction of the complete dorsal shell wall (transversal section, centrifugal). Hoploscaphites nicoletii (Morton, 1842), AMNH-FI-99143, Maastrichtian, Cretaceous, Fox Hills Formation (Loc. 3272), S Dakota, USA. A–C. Prior to the detachment of the living chamber, the dorsal shell wall is already complete and consists of a wrinkle layer, a dorsal outer prismatic layer, a dorsal nacreous layer and a dorsal inner prismatic layer. B. Close-up of A. D. In the detached living chamber, at least a dorsal nacreous layer is formed. The dorsal outer prismatic layer and the dorsal inner prismatic layer are not preserved. Abbreviations: dipl, dorsal inner prismatic layer; dncl, dorsal nacreous layer; dopl, dorsal outer prismatic layer; if, infilling; ipl, inner prismatic layer; ncl, nacreous layer; wl, wrinkle layer.