Perfice gressus meos in semitis tuis
Imperfect plagal mode of Elami because the plagal diathesaron is not reached; the ancient offertorial verses completed the 4th below the finalis e.g. "Exaudi" http://pemdatabase.eu/musical-item/18051
Interestingly, the first 4 neumatic elements are merged in the first syllabe of "Perfice"; the rest of the word take elements from what used to be a double bistropha and clivis episematica of the next word "gressus".
Also of important notice is the notation of a b molle at "inclina", which according to some masters e.g. Aranda should be avoided in order to keep the modal diapente; this however would in turn cause a tritonus F-B#, which in turn to be avoided should force the F to go accidental (F# or "fa diesis"), which would cause a huge distortion at the important structural corda of Ffaut.