Fig. 20 in The dorsal shell wall structure of Mesozoic ammonoids

Fig. 20. Construction of the complete dorsal shell wall of Amaltheidae (A, lateral view, growth direction to the bottom; B, C, transversal section, centrifugal). A. Amaltheus cf. margaritatus de Monfort, 1808, BSPG MAn-100, late Pliensbachian, Jurassic, Eype Mouth, Dorset, England; a spiral ornament covers the overlap area of two whorls; the succeeding whorl was removed. The coated venter of the preceding whorl shows the typical pattern of several spiral lines. B. Amaltheus margaritatus de Monfort, 1808, BSPG MAn-4798, late Pliensbachian, Jurassic, Buttenheim, Bavaria, SE Germany; B1, the dorsal shell wall consists of an outer spiral ornament and inner bunches of prismatic sub-layers that correspond to the dorsal nacreous layer and the dorsal inner prismatic layer; B2, the dorsal nacreous layer transforms into prismatic layers; B3, close-up of B2. C. Pleuroceras salebrosum Hyatt, 1867, BSPG MAn-4804, late Pliensbachian, Jurassic, Buttenheim, Bavaria, SE Germany; the dorsal shell wall forms a spiral ornament. Abbreviations: dipl, dorsal inner prismatic layer; dncl, dorsal nacreous layer; if, infilling; ipl, inner prismatic layer; ncl, nacreous layer; s, septum; so, spiral ornament.