Fig. 4

Internal structure of varices and constrictions (growth direction left). The internal thickening is formed by the nacre layer, the inner prismatic layer becomes thinner in these areas. a, b Euphylloceras sp. (MAo-1769), a asymmetrical varix, b close-up of a, adoral end of varix, only the inner portions of the nacre layer seem to continue; c, d Calliphylloceras sp. (MAn-4511), c symmetrical varix, d close-up of c, adoral end of varix, only the inner portions of the nacre layer seem to continue; e Puzosia saintoursi COLLIGNON (MAo-1792), asymmetric constriction, the outer prismatic layer forms the outer relief which is compensated by the dorsal inner prismatic layer, only the inner lamellae of the nacre layer seem to continue. dipl dorsal inner prismatic layer, ipl inner prismatic layer, ncl nacre layer, opl outer prismatic layer, S septum, wl wrinkle layer