These are polished fossil Goniatite, a close relative of ammonites (same Subclass) that has been polished to reveal the inner chamber detail. These Goniatites are Devonian in age and are quarried from the Atlas Mountains in Morocco.
Goniatites possessed a shell, which is divided internally into chambers filled with gas for buoyancy. An open chamber at the front of the shell provided living space for the animal. The general morphology and habit of goniatites was probably similar to that of their later relatives the ammonites, being free swimming and possessing a head with two well developed eyes and arms.