Fig. 1
From: The internal structure of varices and constrictions in Jurassic and Cretaceous ammonoid shells
General appearance of varices and constrictions (growth direction left). a Varices and constrictions leave furrow imprints on the internal mould. b Varices are formed by internal thickenings of the shell while shell surface remains smooth. c Constrictions are formed by flexures of the shell, often they are accompanied by an internal thickening. ipl inner prismatic layer, ncl nacre layer, opl outer prismatic layer