I'm working on Late Cretaceous carbonates in central southern atlas of Tunisia. I think that these are longitidunal sections of Rudists but I need confirmation and a more detailed description.
As previously stated by Stevens and El Hassi, they are rudists. With those sections is not easy to precise genus or species, but in the first picture at the right side, one of the specimens shows a typical reticulate structure of the wall that copuld be usefulo to identify them.