Here's another interesting fossil that turned up in my storage . . . a Tilly bone that has been sawed in half.
I took some close-ups with my camera (unhappily, my microscope camera software is not compatible with my new Intel Core i5 processor). But, I think you can see the gross structure and identify the bone, a pterygiophora ("ter-RIJ-ee-AH-for-ah", I think).
Tilly bones are bone overgrowths of unknown etiology. This one is from a fish axial skeleton with bilateral symmetry. A pterygiophora is the basal spine (within the fish body) which supports and articulates with the dorsal fin spine on the body exterior.
Show us some more Tilly bones.