Reference edition:

Grammatici Latini, VI. Scriptores artis metricae. Marius Victorinus, Maximus Victorinus, Caesius Bassus etc., ex recensione H. Keilii, Hildesheim 1961, 174-184 (reprografischer Nachdruck der Ausgabe Leipzig 1874).

The text of this short treatise that focuses on the analysis of Horatian metres is contained in three codices from the Carolingian period and is found immediately after the long section that preserves the initial part of Marius Victorinus's Ars grammatica, and which in the manuscript tradition was combined with the treatise de metris that critics tend to attribute to Helios Festus Aphthonius (GLK 6, 1-173). The codices probably date from a 5th-6th century oncial manuscript and are as follows: 1) Vaticanus Palatinus Latinus 1753 (A), membranaceous, IX century, copied at the Benedictine monastery of St. Nazarius in Lorsch; later interventions by a corrector antiquus (A¹) and a corrector recentior (A²) are recognisable; 2) Parisinus Latinus 7539 (B), membranaceous, IX century, copied at the Benedictine monastery of Corbie; in it, the section de re metrica is attributed in its entirety to Marius Victorinus; 3) Valentianus 395 ol. M. 6. 10 (V), membranaceous, IX century, copied at the monastery of Saint-Amande-les-Eaux, apograph of A, of which it completes a lacuna and offers the original text where it is corrected by A², having been copied after A¹ but before A².  Keil's edition was conducted on the basis of the Palatinus and Valentianus. Giuseppe Morelli (1970, p. 28) suggests indicating this treatise, which deliberately refers to the section de metris Horatianis of the Aftonian treatise, with the formula index Horatianus. The subscriptio that closes the index arbitrarily attributes the pamphlet to Marius Victorinus (explicit ars grammatica Victorini Mari de ortographia et de metrica ratione), but Morelli thinks of the work of a fifth-century forger who would have recast his own writing in the miscellany book and proposed it as a thematic appendix to the section de metris by Aftonius. The index consists of a concise introduction, an index of the metres used by Horace in the Odes and Epodes, and a brief disquisition on the differences between ode and melos and between colon and comma. [D. Di Rienzo]