Members of the cephalopod family Nautilidae are commonly called "Nautilus."
Present day nautiluses are the only living members of the subclass Nautiloidea.
Nautiluses belong to an ancient cephalopod family that has survived several severe extinction events that destroyed much other sea life.  A possible reason for the longevity of the nautilus clan is an ability to enter a type of "hibernation" life mode that can bridge long periods of poor environmental conditions.
There is more information at: The Nautilus

The nautilius specimens offered here are from Mahajanga Province, Madagascar.  They date from the mid-Cretaceous Albian Age The specimens were prepared in Madagascar by local native artisans.