The manuscript 3314/15 of the Universitäts- und Landesbibliothek at Darmstadt (originally from Seligenstadt) contains a fragment of a mid-twelfth-century tonary that is essentially identical to interpolations in the tonary of Theoger of Metz transmitted in the manuscript Kassel, 4o Mss. Math. 1. The Seligenstadt tonary is of especial interest, inasmuch as it is one of the first sources to cite differentiae peregrinae in addition to the ordinary differentiae for the psalm tones in each of the ecclesiastical modes. These irregular differentiae were designated ‘peregrinae’ for the first time by Berno. Differentiae peregrinae are occasionally mentioned in the south German cultural sphere during the twelfth century, but by the fourteenth and fifteenth centuries they were being discussed frequently. It is precisely at this time that the fourth differentia of the eighth ecclesiastical mode came to be known as the ‘tonus peregrinus’.