Andrew Neild ( author of Butterflies of Venezuela ):

In helenor the submarginal whitish band on the underside hindwing widens towards the apex and is usually widest at the apex; in achilles it narrows towards the apex, and is usually wider / widest in its mid section. Also, but not always, on the FW, in space 3 ( the one that usually has the biggest FW ocellus ), the broad pale band is almost always crescent-shaped. In achilles it is usually triangular, or if nearly crescent-shaped, wider than it is in sympatric helenor.