who was Heracleides?

[agesilaos]

Unfortunately I don't have a Greek Plutarch only the Penguin translation. But reading it I would say the 'tradition handed down by the Alexandrians' is merely the local story of the foundation of the city and the locals base it on the work of Herakleides, or rather a passage therein. Since the story plutarch tells is connected with Homer a commentary on his works would be a likely source.