Engraving of a nautilus and an ammonite. The nautilus is one of the species of marine cephalopods of the family Nautilidae. There are two genera (Allonautilus and Nautilus), with a total of six species. They grow with a shell that gets larger as they grow. The spiral shell is divided into chambers. Here this is compared with the cross section of an ammonite fossil (top left) found at Whitby, Yorkshire. This engraving was first published in the Gentleman's Magazine in 1752.