Information on differentia
As this manuscript contains the Old Roman repertory of liturgical chant, its differentiae are not part of the octomodal system. In the original Cantus index for this manuscript, differentiae were assigned a letter-number code to indicate the last note of the differentiae within each of the Roman modes. For more on this, see the manuscript description on Cantus.
Mitchell, Andrew. Inventory of Città del Vaticano (Roma), Biblioteca Apostolica Vaticana, San Pietro B.79. Edited by Debra Lacoste. In: Cantus Manuscript Database for Latin Ecclesiastical Chant: Inventories of Chant Sources. Directed by Debra Lacoste (2011-), Terence Bailey (1997-2010), and Ruth Steiner (1987-1996). Web developer, Jan Kolácek (2011-).
Images: Biblioteca Apostolica Vaticana