Hello together,
I just remembered an interesting specimen I have had for many years, my uncle gave it to me when I was a kid. Unfortunately I have no information on its origin. It has some structures that may be diagnostic to the right eye though.
Some pictures of rudists I recently saw reminded me of its general appearance, but now looking at it again I wonder if it is a big gastropod columella. the reddish middle part marked in black is actually standing out much more than the flashlight-picture shows, with cavities left and right that may have connected behind before being covered in calcite. the lower left corner shows some structure, zoomed in on the second pic. there are also some bullet-shaped holes that look like negatives of belemnite rostra or maybe clam borings? (secon pic lower right)
Hoping for your insight,
Best Regards,
J