Agatized trilobite cephalon?

[SilurianSalamander]

Found in Michigan LP. Devonian age probably? Loads of corals and other agatized fossils wash up on that beach. This is the only one I’ve found like this.

[Rockwood]

' not sure what it was, but trilobite doesn't seem right.

[debivort]

perhaps a gastropod, where the cavities are the outer whorl, and the middle has broken away and filled with mud/matrix?