| Noun | 1. | Belemnitidae - family of extinct Mesozoic cephalopods mollusk family - a family of mollusks Belemnoidea, order Belemnoidea - order of extinct dibranchiate cephalopods related to the surviving spirulas belemnite - 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 |