Numbers 3:17-18, 21

And these were the sons of Levi by their names: Gershon and Kohath and Merari. And these are the names of the sons of Gershon by their clans: Libni and Shimei.

To Gershon belonged the clan of the Libnites and the clan of the Shimeites; these were the clans of the Gershonites.