I think I have tracked down what it is.
The fossil remains of turritella are the shells or the cast of shells from soft-bodied mollusks. Turritella are a type of sea snail with tall spiral shells. They vary in size from about 1/2 inch to 6 inches long.

Turritella is a genus of medium-sized sea snails with an operculum, marine gastropod mollusks in the family Turritellidae. They have tightly coiled shells, whose overall shape is basically that of an elongated cone.

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