The figure on the left summarizes the ammonite parts already explained on the Shell description page, on the cross-section of a whorl. In practice, a shoulder may be blunt and only appear as a zone of greater curvature: in that case, the boundary with the flanks is imprecise. It may even be absent: for example, Sonneratia perinflata Breistroffer has a semicircular section, without ventrolateral shoulders.
On the right are shown typical whorl sections from Saveliev (1973a). We have added 17-19. Most terms refer to the overall shape, ignoring the dorsum. The term "oval" is ambiguous: depending on authors, it means either "elliptical" or "ovoid" (egg-shaped), which is the etymological meaning. Similarly, the term "ogival" is often employed for a parabolic ogive, whereas the true ogive (the gothic one) starts from parallel sides converging toward an angular vault. The shapes described are rarely perfect: for example, the rectangular cross-section often has more or less rounded corners. Further details can be added to avoid ambiguity: Are the sides parallel? If not, do they converge or diverge towards the venter? At what height is the maximum thickness located, for example at mid-flank or at the umbilical margin?