The Lexicon Messanense (also known under the name of Orus’ Orthography), is a medieval-era orthographical lexicon whose segments are preserved today in one manuscript, namely cod. Messanensis S. Salv. 118 (14th century) deposited at the University Library of Messina, Italy.
The text of the Lexicon Messanense, published by Rabe [1892; 1895], reveals the remains of a Greek orthographical lexicon, which mostly discusses the presence of iota subscript (iota anekphōnēton) in the orthography of a number of ancient Greek words. The Lexicon is severely mutilated, with many leaves missing; its surviving part preserves entries from the end of letter M to the beginnings of …
Papanikolaou, Dimitrios. "Lexicon Messanense / Orus’ Orthography". The Literary Encyclopedia. First published 22 February 2019
[https://www.litencyc.com/php/stopics.php?rec=true&UID=19558, accessed 23 March 2019.]