It looks like this Part has been superseded by LEGO Part 18866 Clam [Type 2 - Locking Edge on Inner Lip].
Molds 30218 and 18866 has a number of differences:
|1||Scalloped edge||Smooth edge|
|2||Scalloped inner edge||Locking finger on inner edge|
|3||Round (slightly faceted) bar hole||Octagonal bar hole|
|4||Slit on both sides||Slit only on bottom side|
Mold 18866 has better locking power than 30218. Used parts 30218 may even open by themselves.
Click on a colored part below to see the Sets and MOCs that use part 30218 Clam [Type 1 - Continuous Scalloped Inner Lip] in that color. You can find an overview of all LEGO Colors here.