Information on differentia
Differentiae are indicated throughout the manuscript by tonary letters in the margins that refer to a tonary (pp. 2-5), which provides the adiastematic neumes for each of the tonary letters. See 388. This page is based on the second tonary, which was added in the fourteenth century (pp. 495-497) and provides slightly different differentiae but references the same tonary letters. Two differentiae are notated on staff lines in the margins of the manuscript in a later hand for the following antiphons: Laetare Gallia quae tantum virum (p. 480) and Hic est ille Leonardus qui (p. 480). The differentia for Laetare Gallia (mode 4, differentia 41a), does not match the mode 4 antiphons included in either tonary, as transcribed by P. Ephrem Omlin (it rises to a C rather than a B). The differentia for Hic est ille, a mode 5 antiphon, matches the differentia "v" in the manuscript's tonary (differentia 129a). For the rationale of the transcription of adiastematic neumed differentiae into pitched notation, see Rebecca Shaw's thesis. The differentiae in this tonary are also transcribed into pitched notation in P. Ephrem Omlin's Die Sankt-Gallischen Tonarbuchstaben(Regensburg: Friedrich Pustet, 1934).
Hammond, Susanne. Inventory of Sankt Gallen, Stiftsbibliothek, 388. Edited by Andrew Mitchell. 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-). Omlin, P. Ephrem. Die Sankt-Gallischen Tonarbuchstaben. Regensburg: Friedrich Pustet, 1934.
Images: St. Gallen, Stiftsbibliothek, Cod. Sang. 388, pp. 495-497