Fig. 2 in The dorsal shell wall structure of Mesozoic ammonoids

Fig. 2. Schematic drawing of general dorsal shell wall types (A1, B1, transversal section, centrifugal; A2, B2, median section, growth direction left, centrifugal). A. Reduced dorsal shell wall. The lateral shell wall wedges out at the contact with the preceding whorl. The dorsal wall is omitted at the aperture. B. Complete dorsal shell wall. The ventral, lateral, and dorsal shell walls form a continuum. The dorsal wall is present at the aperture. Colouring: black, ventral/lateral wall of the succeeding whorl; dark grey, dorsal wall of the succeeding whorl; light grey, septum of the succeeding whorl; white, ventral wall of the preceding whorl.