Quispel Suggests a Part of Irenaeus's Treatise Against Valentinus Came From Justin's Syntagma

It continues to be plausible that Irenaeus used the (updated) Syntagma of Justin for his catalogue of heresies. And it would seem that the chapter about Valentinus himself, as distinguished from his pupils (1.11.1), was taken over from the same source, because here, as in the other chapters of the catalogue, the name of the heresiarch is mentioned before his teaching is expounded (this is not the case in 1.29–30). But then this report is extremely valuable, because it has been written by a contemporary of Valentinus, who lived in the same city, Rome, and like him had some notion of the (Middle) Platonic philosophy of his day. [Gilles Quispel Gnostica, Judaica, Catholica p. 370] 

Here is the section in Irenaeus's Against Heresy to which Quispel draws our attention

Let us now look at the inconsistent opinions of those heretics (for there are some two or three of them), how they do not agree in treating the same points, but alike, in things and names, set forth opinions mutually discordant. The first of them, Valentinus, who adapted the principles of the heresy called "Gnostic" to the peculiar character of his own school, taught as follows: He maintained that there is a certain Dyad (twofold being), who is inexpressible by any name, of whom one part should be called Arrhetus (unspeakable), and the other Sige (silence). But of this Dyad a second was produced, one part of whom he names Pater, and the other Aletheia. From this Tetrad, again, arose Logos and Zoe, Anthropos and Ecclesia. These constitute the primary Ogdoad. He next states that from Logos and Zoe ten powers were produced, as we have before mentioned. But from Anthropos and Ecclesia proceeded twelve, one of which separating from the rest, and falling from its original condition, produced the rest of the universe. He also supposed two beings of the name of Horos, the one of whom has his place between Bythus and the rest of the Pleroma, and divides the created AEons from the uncreated Father, while the other separates their mother from the Pleroma. Christ also was not produced from the AEons within the Pleroma, but was brought forth by the mother who had been excluded from it, in virtue of her remembrance of better things, but not without a kind of shadow. He, indeed, as being masculine, having severed the shadow from himself, returned to the Pleroma; but his mother being left with the shadow, and deprived of her spiritual substance, brought forth another son, namely, the Demiurge, whom he also styles the supreme ruler of all those things which are subject to him. He also asserts that, along with the Demiurge, there was produced a left-hand power, in which particular he agrees with those falsely called Gnostics, of whom to we have yet to speak. Sometimes, again, he maintains that Jesus was produced from him who was separated from their mother, and united to the rest, that is, from Theletus, sometimes as springing from him who returned into the Pleroma, that is, from Christ; and at other times still as derived from Anthropos and Ecclesia. And he declares that the Holy Spirit was produced by Aletheia for the inspection and fructification of the AEons, by entering invisibly into them, and that, in this way, the AEons brought forth the plants of truth.

It is worth noting that this material is not reproduced in Tertullian's copy of Irenaeus's original 'Against the Valentinians.'   Indeed it is interesting to note that the Philosophumena does not reproduce this section either but both the Philosophumena and Against the Valentinians reproduce what immediately follows about 'Secundus' (1.11.2 - 5) albeit Against the Valentinians in a completely different order.