Justin mentions writings (Memorabilia) called Gospels thrice:
Justin Martyr, 1 Apology 66.3-4: 3 For the apostles, in the Memorabilia made by them, which are called Gospels, have thus delivered unto us what was enjoined upon them, that Jesus took bread and, when He had given thanks, said, “This do in memory of Me; this is My body,” and that, after the same manner, having taken the cup and given thanks, He said, “This is My blood,” and gave it to them alone, 4 which the wicked demons have imitated in the mysteries of Mithras, commanding the same thing to be done. For, that bread and a cup of water are placed with certain incantations in the mystic rites of one who is being initiated, you either know or can learn. / 3 Οἱ γὰρ ἀπόστολοι ἐν τοῖς γενομένοις ὑπ´ αὐτῶν ἀπομνημονεύμασιν, ἃ καλεῖται εὐαγγέλια, οὕτως παρέδωκαν ἐντετάλθαι αὐτοῖς, τὸν Ἰησοῦν λαβόντα ἄρτον εὐχαριστήσαντα εἰπεῖν, «Τοῦτο ποιεῖτε εἰς τὴν ἀνάμνησίν μου· τοῦτ´ ἐστι τὸ σῶμά μου,» καὶ τὸ ποτήριον ὁμοίως λαβόντα καὶ εὐχαριστήσαντα εἰπεῖν, «Τοῦτό ἐστι τὸ αἷμά μου,» καὶ μόνοις αὐτοῖς μεταδοῦναι, 4 ὅπερ καὶ ἐν τοῖς τοῦ Μίθρα μυστηρίοις παρέδωκαν γίνεσθαι μιμησάμενοι οἱ πονηροὶ δαίμονες. ὅτι γὰρ ἄρτος καὶ ποτήριον ὕδατος τίθεται ἐν ταῖς τοῦ μυουμένου τελεταῖς μετ´ ἐπιλόγων τινῶν, ἢ ἐπίστασθε ἢ μαθεῖν δύνασθε.
Justin Martyr, Dialogue 10.1-4: 1 And when they ceased, I again addressed them thus, “Is there any other matter, my friends, in which we are blamed than this, that we do not live according to the Law and are not circumcised in the flesh as your forefathers were, and we do not observe Sabbaths as you do? Are our lives and customs also slandered among you? And I ask this. Have you also believed concerning us that we eat men; and that after the feast, having extinguished the lights, we engage in promiscuous concubinage? Or do you condemn us in this alone, that we adhere to such tenets, and believe in an opinion, untrue, as you think?” 2 “This is what we are amazed at,” said Trypho, “but those things about which the multitude speaks are not worthy of belief, for they are most repugnant to human nature. Moreover, I am aware that your precepts in the so called Gospel are so wonderful and so great that I suspect no one can keep them, for I have carefully read them. 3 But this is what we are most at a loss about: that you, professing to be pious and supposing yourselves better than others, are not in any particular separated from them, and you do not alter your mode of living from the nations in that you observe no festivals or Sabbaths and do not have the rite of circumcision; and further, resting your hopes on a man that was crucified, you yet expect to obtain some good thing from God while you do not obey His commandments. Have you not read, ‘That soul shall be cut off from his people who shall not have been circumcised on the eighth day’ (= Genesis 17.14)? And this has been ordained for strangers and for slaves equally. 4 But you, despising this covenant rashly, reject the consequent duties and attempt to persuade yourselves that you know God, when, however, you perform none of those things which they do who fear God. If, therefore, you can defend yourself on these points and make it manifest in what way you hope for anything whatsoever, even though you do not observe the Law, this we would very gladly hear from you, and we shall make other similar investigations.” / 1 Ὡς δὲ ἀνεπαύσαντο, ἐγὼ οὕτως αὐτοῖς πάλιν ἠρξάμην, «Μὴ ἄλλο τί ἐστιν ὃ ἐπιμέμφεσθε ἡμᾶς, ἄνδρες φίλοι, ἢ τοῦτο ὅτι οὐ κατὰ τὸν νόμον βιοῦμεν, οὐδὲ ὁμοίως τοῖς προγόνοις ὑμῶν περιτεμνόμεθα τὴν σάρκα, οὐδὲ ὡς ὑμεῖς σαββατίζομεν; ἢ καὶ ὁ βίος ἡμῶν καὶ τὸ ἦθος διαβέβληται παρ´ ὑμῖν; τοῦτο δ´ ἐστὶν ὃ λέγω, μὴ καὶ ὑμεῖς πεπιστεύκατε περὶ ἡμῶν, ὅτι δὴ ἐσθίομεν ἀνθρώπους καὶ μετὰ τὴν εἰλαπίνην ἀποσβεννύντες τοὺς λύχνους ἀθέσμοις μίξεσιν ἐγκυλιόμεθα, ἢ αὐτὸ τοῦτο καταγινώσκετε ἡμῶν μόνον, ὅτι τοιούτοις προσέχομεν λόγοις καὶ οὐκ ἀληθεῖ, ὡς οἴεσθε, πιστεύομεν δόξῃ;» 2 «Τοῦτ´ ἔστιν ὃ θαυμάζομεν,» ἔφη ὁ Τρύφων, «περὶ δὲ ὧν οἱ πολλοὶ λέγουσιν, οὐ πιστεῦσαι ἄξιον· πόρρω γὰρ κεχώρηκε τῆς ἀνθρωπίνης φύσεως. ὑμῶν δὲ καὶ τὰ ἐν τῷ λεγομένῳ εὐαγγελίῳ παραγγέλματα θαυμαστὰ οὕτως καὶ μεγάλα ἐπίσταμαι εἶναι, ὡς ὑπολαμβάνειν μηδένα δύνασθαι φυλάξαι αὐτά· ἐμοὶ γὰρ ἐμέλησεν ἐντυχεῖν αὐτοῖς. 3 ἐκεῖνο δὲ ἀποροῦμεν μάλιστα, εἰ ὑμεῖς, εὐσεβεῖν λέγοντες καὶ τῶν ἄλλων οἰόμενοι διαφέρειν, κατ´ οὐδὲν αὐτῶν ἀπολείπεσθε, οὐδὲ διαλλάσσετε ἀπὸ τῶν ἐθνῶν τὸν ὑμέτερον βίον, ἐν τῷ μήτε τὰς ἑορτὰς μήτε τὰ σάββατα τηρεῖν μήτε τὴν περιτομὴν ἔχειν, καὶ ἔτι, ἐπ´ ἄνθρωπον σταυρωθέντα τὰς ἐλπίδας ποιούμενοι, ὅμως ἐλπίζετε τεύξεσθαι ἀγαθοῦ τινος παρὰ τοῦ θεοῦ, μὴ ποιοῦντες αὐτοῦ τὰς ἐντολάς. ἢ οὐκ ἀνέγνως, ὅτι ‹Ἐξολοθρευθήσεται ἡ ψυχὴ ἐκείνη ἐκ τοῦ γένους αὐτῆς, ἥτις οὐ περιτμηθήσεται τῇ ὀγδόῃ ἡμέρᾳ;› ὁμοίως δὲ καὶ περὶ τῶν ἀλλογενῶν καὶ περὶ τῶν ἀργυρωνήτων διέσταλται. 4 ταύτης οὖν τῆς διαθήκης εὐθέως καταφρονήσαντες ὑμεῖς ἀμελεῖτε καὶ τῶν ἔπειτα, καὶ πείθειν ἡμᾶς ἐπιχειρεῖτε ὡς εἰδότες τὸν θεόν, μηδὲν πράσσοντες ὧν οἱ φοβούμενοι τὸν θεόν. εἰ οὖν ἔχεις πρὸς ταῦτα ἀπολογήσασθαι, καὶ ἐπιδεῖξαι ᾧτινι τρόπῳ ἐλπίζετε ὁτιοῦν, κἂν μὴ φυλάσσοντες τὸν νόμον, τοῦτό σου ἡδέως ἀκούσαιμεν μάλιστα, καὶ τὰ ἄλλα δὲ ὁμοίως συνεξετάσωμεν.»
Justin Martyr, Dialogue 100.1: 1 And the following, “But You, the praise of Israel, inhabit the holy place” (= Psalm 22.3) declared that He is to do something worthy of praise and wonderment, being about to rise again from the dead on the third day after the crucifixion; and this He has obtained from the Father. For I have showed already that Christ is called both Jacob and Israel; and I have proved that it is not in the blessing of Joseph and Judah alone that what relates to Him was proclaimed mysteriously, but also in the Gospel it is written that He said, “All things are delivered unto me by My Father” (= Matthew 11.27a), and, “No man knows the Father but the Son, nor the Son but the Father, and those to whom the Son will reveal Him” (= Matthew 11.27b). / 1 Τὸ δὲ ἀκόλουθον, «Σὺ δὲ ἐν ἁγίῳ κατοικεῖς, ὁ ἔπαινος τοῦ Ἰσραήλ,» ἐσήμαινεν ὅτι ἐπαίνου ἄξιον καὶ θαυμασμοῦ μέλλει ποιεῖν, μετὰ τὸ σταυρωθῆναι ἀνίστασθαι μέλλων τῇ τρίτῃ ἡμέρᾳ ἐκ νεκρῶν, ὃ ἀπὸ τοῦ πατρὸς αὐτοῦ λαβὼν ἔχει. ὅτι γὰρ καὶ Ἰακὼβ καὶ Ἰσραὴλ καλεῖται ὁ Χριστός, ἀπέδειξα· καὶ οὐ μόνον ἐν τῇ εὐλογίᾳ καὶ Ἰωσὴφ καὶ Ἰούδα τὰ περὶ αὐτοῦ κεκηρύχθαι ἐν μυστηρίῳ ἀπέδειξα, καὶ ἐν τῷ εὐαγγελίῳ δὲ γέγραπται εἰπών, «Πάντα μοι παραδέδοται ὑπὸ τοῦ πατρός,» καὶ, «Οὐδεὶς γινώσκει τὸν πατέρα εἰ μὴ ὁ υἱός, οὐδὲ τὸν υἱὸν εἰ μὴ ὁ πατὴρ καὶ οἷς ἂν ὁ υἱὸς ἀποκαλύψῃ.»