This article deals with four Greek leaves in Arabic oriental paper that transmit some Psellian letters and are here identified as formerly belonging to the current Vat. Barb. gr. 240. These sheets today represent fols. 372-375 of the codex Allacci XCI kept in the Biblioteca Vallicelliana in Rome. A palaeographic analysis has also allowed us to recognize in the marginal notes contained in these folia the Greek script of the famous scholar Leo Allatius, and to identify in some leaves of Vat. gr. 1912 (unit n° VIII) – another witness to the Psellian letters – the handwriting (Greek and Latin) of the copyist Simon Portius. This paper ends by providing a content description of the four folia.