Fig. 7
From: The internal structure of varices and constrictions in Jurassic and Cretaceous ammonoid shells
Discontinuities associated with varices (growth direction left). a, b Eotetragonites umbilicostriatus COLLIGNON (MAo-1776), a normal asymmetric varix, the internal thickening is formed by the nacre layer, the inner prismatic layer becomes thinner in that area, b young varix associated with a flare, the first shell generation is bent outward (opl 1 and ncl 1), the second shell generation forms the actual varix (opl 2 and ncl 2); c, d E. umbilicostriatus COLLIGNON (MAo-1773); c adoral end of a varix with slight discontinuity in the outer shell portions, a first generation of the outer prismatic layer and nacre layer (opl 1 and ncl 1) can be distinguished from a second one (opl 2 and ncl 2), the inner prismatic layer is not affected, d malformation associated with the adoral end of a varix, a first generation of the outer prismatic layer and nacre layer (opl 1 and ncl 1) can be distinguished from a second one (opl 2 and ncl 2), the first shell generation ends abruptly at a vertical edge, the inner prismatic layer is not affected. dipl dorsal inner prismatic layer, ipl inner prismatic layer, ncl, ncl 1, ncl 2 nacre layer, opl, opl 1, opl 2 outer prismatic layer, S septum, pel pelicula, wl wrinkle layer