The manuscript tradition for the fragment in the title gives us:
ἔλθοντ' ἐξ ὀράνω πορφυρίαν ἔχοντα προϊέμενον χλάμυν
For reasons of meter, deleting the ἔχοντα is basically mandatory. However, why do Lobel-Page and Campbell emend the participle προϊέμενον to the very different περθέμενον instead of simply removing the troublesome umlaut and reading προιέμενον like Edmonds does? This reading is closer to the tradition, so why discard it? Is there any critical or linguistic reason to do so, or is it just that "clad in" a mantle is in a sense easier to picture than "sending forth" a mantle?