The descendants of Caleb (Jerahmeel’s brother) were his firstborn son Mesha, who first settled Ziph, and the sons of Mareshah, who first settled Hebron.
Achish would ask, “Whom did you raid today?” And David would answer, “the Negev in Judah,” or “the portion of the Negev where the descendants of Jerahmeel live,” or “the portion of the Negev where the Kenites live.”