18 These were the names of the Gershonite clans: Libni and Shimei.

Read Numbers 3:18 Using Other Translations

And these are the names of the sons of Gershon by their families; Libni, and Shimei.
And these are the names of the sons of Gershon by their clans: Libni and Shimei.
The clans descended from Gershon were named after two of his descendants, Libni and Shimei.