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 oblique or parallel to the axis of coiling (horizontal), sparse or numerous, easily discernible, or deeply embedded within the shell such that they are only visible in broken shells. When the axis of coiling is hollow (perforate spire) the base opening serves as the umbilicus.