The Epiklesis in the liturgies was added in the fourth century and evidence exists that it was present in the Roman Mass in the fifth. “We may then surely conclude that in the Vth century Rome had an Invocation of the Holy Ghost.” But, it “was removed at Rome, apparently deliberately, because of the growing Western insistence on the words of institution as the Consecration form.” And “It is however generally admitted that our difficult " Supplices te rogamus " prayer represents a fragment of the old Epiklesis, with the essential clause left out”. “The normal place of the Epiklesis is after the words of institution, at the end of the Anamnesis (so in all extant rites). This place seems to be fixed because the Anamnesis, mentioning the Ascension, leads naturally to the memory of Pentecost and so to the Holy Ghost (above p. 346).”
The Mass A Study of the Roman Liturgy by Adrian Fortescue. Longmans, Green And Co. 39 Paternoster Row, London, New York, Bombay And Calcutta, 1914. (From Appendix II, The Epiklesis).
archive.org/stream/massstudyofroman00fort/massstudyofroman00fort_djvu.txt