1) Phragma cone 1) Phragmacone 2) Shell 
The phragmocone is the chambered portion of the shell of a cephalopod. It is divided by septa into camerae. In most nautiloids and ammonoids, the phragmocone is a long, straight, curved, or coiled structure, in which the camarae are linked by a siphuncle which determines buoyancy by means of gas exchange. Despite this benefit, such a large shell a...
• (n.) The thin chambered shell attached to the anterior end of a belemnite.
Phrag'mo·cone noun [ Greek ..., ..., a fence, an inclosure + ... a cone.] (Zoology) The thin chambered shell attached to the anterior end of a belemnite. [ Written also phragmacone .]
[n] - the thin conical chambered internal shell (either straight or curved) of a belemnite
phragmacone noun the thin conical chambered internal shell (either straight or curved) of a belemnite