Cymatoceras are nautiloids that lived from the Jurassic to the Oligocene. Its shell is made of two layers--the innermost being iridescent and the outer layer providing protection. The interior have partitions that divide the shell into compartments, which help the animal maintain buoyancy.
Phylum Mollusca, Class Cephalopoda
Subclass Nautiloidea, Order Nautilida
Middle Cretaceous, Albian Stage (112 million years ago)
Size: 5.75 x 4.94 x .81 inches
Weight: 1.9 lbs.