This is a single chamber from a nautilus. The shell itself is not preserved; all that is preserved is the hollow space contained within one single chamber. The faint hole in the middle of the structure is where the syphuncle, a tube connecting all the chambers together, passed through the chamber wall. A series of these bizarre sections would fit together to form the coiled chambered shell. The additional image below is of a modern nautilus shell cut in half to show the chambers within the shell.
