[Hermann the Cherusker]

Supposedly there is a letter of St. Gelasius I that refers to an epiclesis in the Roman Canon. The Roman Canon certainly had a different original order than it does today.

[Tantumergo]

"Supposedly there is a letter of St. Gelasius I that refers to an epiclesis in the Roman Canon."

Fine, but as I said in a later post, the Quam oblationem, could be taken as an implicit epiclesis - what form did it take under Gelasius? Was it an explicit invocation of the Holy Ghost which the Roman Rite subsequently dropped?

"The Roman Canon certainly had a different original order than it does today."

It quite possibly did - I would be interested to see the earliest form of it.