Passage 9.5.3
ἐπὶ μὲν δὴ Κάδμου μέγιστον μετά γε αὐτὸν Κάδμον ἠδύναντο οἱ Σπαρτοί, Χθόνιος καὶ Ὑπερήνωρ καὶ Πέλωρος καὶ Οὐδαῖος· Ἐχίονα δὲ ὡς προέχοντα κατʼ ἀνδραγαθίαν γαμβρὸν ἠξίωσεν ὁ Κάδμος ποιήσασθαι. τοὺς δὲ ἄνδρας τούτους---οὐ γάρ τι ἠδυνάμην ἐς αὐτοὺς παρευρεῖν---ἕπομαι τῷ μύθῳ Σπαρτοὺς διὰ τὸν τρόπον ὅντινα ἐγένοντο ὀνομασθῆναι. Κάδμου δὲ ἐς Ἰλλυριοὺς καὶ Ἰλλυριῶν ἐς τοὺς καλουμένους Ἐγχελέας μετοικήσαντος Πολύδωρος ὁ Κάδμου τὴν ἀρχὴν ἔσχε.
During the reign of Cadmus, next to Cadmus himself the greatest in power were the Sparti—Chthonius, Hyperenor, Pelorus, and Udaeus. But it was Echion who excelled so greatly in valour that Cadmus considered him worthy to become his son-in-law. Regarding these men—since I myself have been unable to find any definite confirmation—I therefore follow the tradition naming them "Sparti" from the manner of their birth. When Cadmus migrated to the Illyrians and specifically to the people called Encheleans among them, Polydorus, the son of Cadmus, took over the kingship.