Fig. 17 in The dorsal shell wall structure of Mesozoic ammonoids

Fig. 17. Construction of the complete dorsal shell wall (median section, growth direction to the left, centrifugal). A. Choffatia (Grossouvria) sp. 1, BSPG MAn-4520, late Callovian, Jurassic, Dubki near Saratov, Russia; A1, the dorsal shell wall consists of a dorsal outer prismatic layer, a dorsal nacreous layer and a dorsal inner prismatic layer; A2, close-up of A1. B. Divisosphinctes besairiei Collignon, 1960, BSPG PA-10151b, late Oxfordian, Jurassic, Sakaraha, Morondava Basin, SW Madagascar; B1, the ventral shell wall (vsw) is overgrown by an encruster (enc) which is in turn overgrown by the succeeding whorl (dsw); B2, the thin early complete dorsal shell is formed in contact with the ventral shell wall; it consists of (a wrinkle layer), a dorsal outer prismatic layer, a dorsal nacreous layer and a dorsal inner prismatic layer; B3, the dorsal outer prismatic layer; B4, the older, thick, detached dorsal shell wall consists of the same three layers as in B2; B5, close-up of B4. Abbreviations: dipl, dorsal inner prismatic layer; dncl, dorsal nacreous layer; dopl, dorsal outer prismatic layer; dsw, dorsal shell wall; enc, encruster; if, infilling; ncl, nacreous layer; opl, outer prismatic layer; s, septum; vsw, ventral shell wall; wl, wrinkle layer.