The critical edition of this treatise, which is dated circa 1271, was created in consultation with two primary manuscripts: Bamberg, Staatliche Bibliothek, Lit. 115 and Trier, Seminarbibliothek, 44. Other manuscripts include portions of the treatise (e.g., Oxford, Bodleian Library, Bodley 77; and Rome, Vatican City, Biblioteca Apostolica Vaticana, ms lat. 5318). Written by Amerus, it contains a tonary (sections 9 to 13). Each of the differentia included are also found in the antiphoners listed in the Appendix. Significantly, Amerus divides differentiae not only by mode but also liturgical use and location. This treatise is not translated and remains in its original Latin.
Amerus. Practica Artis Musicae. Edited by Cesarino Ruini. Neuhausen-Stuttgart: American Institute of Musicology, 1977.