Dear Benjamin,
It is likely you have collected a shell of the genus
Stomatella, family Stomitellidae, superfamily Trochoidea.
Many species look remarkably like abalones, and can easily
be mistaken for them. Since they are, technically, top shells,
they all have a pearly interior, which can cause further confusion.
Freak abalones have been known to lack holes, but it's not very likely
that's what you have, especially if you received two.

Kind Regards,
James