Passage 9.5.16
Αὐτεσίωνος δὲ ἀπελθόντος, οὕτω βασιλέα εἵλοντο Δαμασίχθονα Ὀφέλτου τοῦ Πηνέλεω. τούτου δὲ ἦν τοῦ Δαμασίχθονος Πτολεμαῖος, τοῦ δὲ Ξάνθος, ὃν Ἀνδρόπομπος μονομαχήσαντά οἱ δόλῳ καὶ οὐ σὺν τῷ δικαίῳ κτείνει. τὸ δὲ ἐντεῦθεν διὰ πλειόνων πολιτεύεσθαι μηδὲ ἀπʼ ἀνδρὸς ἑνὸς ἠρτῆσθαι τὰ πάντα ἄμεινον ἐφαίνετο τοῖς Θηβαίοις.
After the departure of Autesion, they thus chose Damasichthon, son of Opheltes, son of Peneleus, as king. Ptolemaeus was the son of this Damasichthon, and Xanthus was the son of Ptolemaeus. Andropompus killed this Xanthus, having fought against him in single combat, treacherously and not justly. After this event, it seemed preferable to the Thebans to have government by many rather than for everything to depend upon the authority of a single individual.