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a genus of extinct unicellular organisms of the subclass Foraminifera. Remains of Nummulites have been found in Upper Cretaceous and in Paleogene deposits in the tropics and subtropics of Europe, Asia, Africa, and America. Nummulites had a lenticular or discoid shell with a diameter that ranged from 1 to 16 cm. The shell contains many whorls divided by septa into chambers; each new whorl completely overlaps the next older whorl. Nummulites led a benthopelagic mode of life. Aggregates of their shells formed nummulitic limestone, which is used as a building material. Nummulites are important index fossils in the stratigraphy of the Paleogene.