Irenaeus’ famous page on the Fourfold Gospel is one of the passages in the Adversus haereses that is known to us from the greatest number of Greek witnesses. However, their textual value is on average rather low. For, as a comparison with the Latin version shows, they transmit Irenaeus’ text in abbreviated or partially—or even, in some cases, extensively—rewritten forms. Moreover, even combining all the evidence we have so far, there are three brief passages from Adv. haer. 3,11,8 which are preserved only in Latin. In the introduction to Book 3 in the Sources chrétiennes edition, published in 1974, Louis Doutreleau concluded:
‘Contemporary research has not succeeded in finding them: it is probable that the ancients did not transmit them to us.’ 
This pessimism was unjustified: I am pleased to announce that there is indeed one Greek witness that preserves them and that, more generally, provides a text of high quality, as attested by its numerous agreements with the Latin version.
This ‘new’ witness is none other than Sevastianov 56 (and not 55), a manuscript from the Russian State Library in Moscow.  Therefore, it is not entirely new, in the sense that it was known and exploited by the editors of the Sources Chrétiennes (Fr. Sagnard, first, then A. Rousseau and L. Doutreleau). However, unbeknownst to them, they only knew the first page, whereas the text continues for two and a half pages, up to the beginning of 11,9, which makes this extract one of the most complete Greek witnesses of Adv. haer. 3,11,8(-9)!
The text of one of these pages is unfortunately very damaged and difficult to read on the digital reproductions made available by the Russian State Library. Nevertheless,it is already possible to provide a provisional edition of the fragment, pending a better transcription of the page in question. This is what I have set out to do in an article entitled ‘Un fragment grec incomplètement exploité d’Irénée (Adv. haer. III, 11, 8) [An Incompletely Exploited Greek fragment of Irenaeus],’ to be published shortly in the Revue des études grecques (135/2 ), in which I also seek to understand how is it that the greater part of this extract has remained ignored for so long.
This post is also an opportunity to point out an interesting article recently published by Agnès Lorrain (CNRS), who explores the tradition of an as yet unpublished Italo-Greek preface to the Gospels, which also derives from this famous page of Irenaeus: ‘Variations italo-grecques sur les Quatre Vivants : les récritures du copiste Leon dans quelques tétraévangiles [Italo-Greek Variations on the Four Living Ones: the Rewritings of the Copyist Leo in Some Four Gospel Manuscripts],’ Νέα Ῥώμη. Rivista di ricerche bizantinistiche 18, 2021, pp. 119–150.
 ‘La recherche contemporaine n’est pas parvenue à les trouver : il est probable que les anciens ne nous les ont pas transmis’ (SC 210, p. 95).