- A conical calcareous fossil, tapering to a point at the
lower extremity, with a conical cavity at the other end, where it is
ordinarily broken; but when perfect it contains a small chambered cone,
called the phragmocone, prolonged, on one side, into a delicate concave
blade; the thunderstone. It is the internal shell of a cephalopod
related to the sepia, and belonging to an extinct family. The
belemnites are found in rocks of the Jurassic and Cretaceous ages.
Definition
[ n.]