Wikipedia
Belemnitella is a genus of belemnite from the Late Cretaceous of Europe and North America. Belemnitella was a squidlike animal, probably related to the ancestors of modern squids and cuttlefish. The shell was internal. The rostrum or guard is found the most often and possesses a distinctive slit at its ventral surface and a ridge on the dorsal surface. The phragmocone (internal shell) has a small protoconch at its tip, and fit into the cavity and the guard. It also had septa and a ventral siphuncle (tube filled with living tissues running through chambers) within the phragmocone, projecting forward as a beak-like blade.
It had growth layers like tree rings, seen within the cavity of the organism and when the cone is sectioned. The cone was light-brown and glassy in appearance. It is distributed widely in North America. A specimen of a belemnoid had been found in Germany, clearly preserving 10 tentacles as carbon films, showing that belemnoids are similar to squids.