These may be oblique or normal to the axis of coiling (horizontal), few or numerous, readily seen, or far within the shell so as to be invisible except in broken shells. When the axis of coiling is hollow (perforate spire) the opening at the base constitutes the umbilicus.
These may be indirect or direct to the axis of coiling (horizontal), few or many, easily seen, or deeply within the shell so as to be invisible except in broken shells. When the axis of coiling is hollow (perforate spire) the opening at the base functions as the umbilicus.