n. 箭石

[ noun ]
a conical calcareous fossil tapering to a point at one end and with a conical cavity at the other end containing (when unbroken) a small chambered phragmocone from the shell of any of numerous extinct cephalopods of the family Belemnitidae
<noun.animal>

Belemnite \Be*lem"nite\, n. [Gr. ? dart, fr. ? dart, fr. ? to
throw: cf. F. b['e]lemnite.] (Paleon.)
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. --
{Bel*em*nit"ic}, a.