De institutione musica IV.16: Descriptio continens modorum ordinem ac differentias.
The preceding diagram bears the names of the strings written beside them, while the added names indicate the notes set alongside them and the mode to which each belongs, whether Lydian, Phrygian or Dorian. But since we have said that these modes are found in the species of the octave, come, let us describe the same modes in the diatonic genus alone, so that their order may fall under the eye and not delay understanding.