Passage 2.18.4
μόνους δὲ Ἑλλήνων οἶδα Ἀργείους ἐς τρεῖς βασιλείας νεμηθέντας. ἐπὶ γὰρ τῆς ἀρχῆς τῆς Ἀναξαγόρου τοῦ Ἀργείου τοῦ Μεγαπένθους μανία ταῖς γυναιξὶν ἐνέπεσεν, ἐκφοιτῶσαι δὲ ἐκ τῶν οἰκιῶν ἐπλανῶντο ἀνὰ τὴν χώραν, ἐς ὃ Μελάμπους ὁ Ἀμυθάονος ἔπαυσε σφᾶς τῆς νόσου, ἐφʼ ᾧ τε αὐτὸς καὶ ὁ ἀδελφὸς Βίας Ἀναξαγόρᾳ τὸ ἴσον ἕξουσιν. ἀπὸ μὲν δὴ Βίαντος βασιλεύουσι πέντε ἄνδρες ἐπὶ γενεὰς τέσσαρας ἐς Κυάνιππον τὸν Αἰγιαλέως, ὄντες Νηλεῖδαι τὰ πρὸς μητρός, ἀπὸ δὲ Μελάμποδος γενεαί τε ἓξ καὶ ἄνδρες ἴσοι μέχρις Ἀμφιλόχου τοῦ Ἀμφιαράου·
The Argives are the only Greeks I know who divided their kingdom into three parts. For during the reign of Anaxagoras, son of Megapenthes, madness came upon the women; rushing forth from their homes, they wandered about the countryside. Melampus, son of Amythaon, relieved them of their affliction, upon the condition that he himself and his brother Bias should share power equally with Anaxagoras. From Bias there descended five kings through four generations to Cyanippus, son of Aigialeus, who were Neleids through their mother. From Melampus descended six generations with an equal number of kings down to Amphilochus, son of Amphiaraus.