[Illustration: FIG. 17.--Internal Shells of Cephalopoda.
A, _Conoteutliis dupiniana_, d'Orb. (from the Neocomian of France).
B, Shell _Sepia orbigniana_. Fér. (Mediterranean).
C, Shell of _Spirulirostra Bellardii_, d'Orb. (from the Miocene of
Turin). The specimen is cut so as to show in section the chambered
shell and the laminated "guard" deposited upon its surface.