These were the subclans descended from the Perezites: The Hezronites, named after their ancestor Hezron. The Hamulites, named after their ancestor Hamul.
The sons of Judah were Er, Onan, Shelah, Perez, and Zerah (though Er and Onan had died in the land of Canaan). The sons of Perez were Hezron and Hamul.
These were the clans descended from Judah’s surviving sons: The Shelanite clan, named after their ancestor Shelah. The Perezite clan, named after their ancestor Perez. The Zerahite clan, named after their ancestor Zerah.