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Following the species of simple septa and straight shells, came the Trocholites ammoulus, of simple septa and coiled chambered shells of the Trenton period.

Coiled Chambered Shell

Following the species of simple septa and straight shells, came the Trocholites ammoulus, of simple…

An illustration of a Spirolina, a sculptured imperfectly coiled shell.

Spirolina

An illustration of a Spirolina, a sculptured imperfectly coiled shell.