SB 8.1.27
caturtha uttama-bhrata
manur namna ca tamasah
prthuh khyatir narah ketur
ity adya dasa tat-sutah
Translation by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada:
The brother of the third Manu, Uttama, was celebrated by the name Tamasa, and he became the fourth Manu. Tamasa had ten sons, headed by Prthu, Khyati, Nara and Ketu.