Turritella

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.
The name "Turritella" comes from the Latin word "turritus" meaning "turreted" or "towered" and the diminutive suffix "-ella".
Species.
Valid.
Valid species within the genus "Turritella" are listed below. Fossil species are marked with a dagger "†".
Invalid.
These are species assigned to "Turritella" that were brought into synonymy with other taxa:
Fossil species.
The genus is known from the Cretaceous to the Recent periods.
The shells are quite frequently found as fossils, and the carbonate stone made from large quantities of "Turritella" shells is often referred to as "Turritella limestone", or, if silicified, "Turritella agate". Both varieties of this stone are commonly sold as polished cabochons.
"Turritella agate".
One variety of "Turritella agate", that from the Green River Formation in Wyoming, is a fossiliferous rock which does indeed contain numerous high-spired snail shells. However, contrary to the common name, these snails are not in the marine genus "Turritella", instead they are freshwater snails in the species "Elimia tenera", family Pleuroceridae from the Eocene epoch. The rock in which these snail shells are so abundant varies from a soft sandstone to a dense chalcedony. This dense silicified rock is popular with gem and mineral hobbyists, as well as with New Age practitioners.
Turritellenplatte.
The "Erminger Turritellenplatte" (""Turritella" plate of Ermingen") near Ulm, Germany is a rocky outcrop situated in the northern part of the North Alpine Foreland Basin. It is famous for its superabundance of "Turritella turris" shells within its sediments and dates from the Burdigalian.