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Haliotis sp.
All found on various beaches on Catalina Island, California.
You have received two ID suggestions. If you cannot decide which is correct, you can update this spotting to include "Haliotis sp." since both are from the same genus. It's not necessary to ID to the species level.
This is not Haliotis varia, as that species would not be found anywhere near Catalina. It is more than likely Haliotis walallensis (Flat Abalone), but it would be much easier to tell by seeing it live. Were these shells purchased or found?