I have been very puzzled about this fossil in particular compared to the other fossils I have. I found it at Manasota Key in Florida in the sea. it seems to be a roof of a mouth of something but I am not sure what (especially considering the small size). Definitely different compared to the fossils of sharks teeth and other mouth parts I had found.

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I'm pretty sure that is a shell of some description. It looks familiar but annoyingly I can't quite place the name right now. It would likely be something close to barnacles.