Ptolemy was a Gnostic philosopher, in whom, according to St. Irenaeus (Proef. ad lib. i, Adv. Hoer.), the system of Valentinus reached its bloom. Irenseus gives a full exposition of it in his work Adv. Hoereses, lib. i, c. i, 8. Ptolemy is also named by Tertullian, but without any particulars of his history (Contr. Valent. c. 33), and in a very few words by Philaster (Her. c. 39), Augustine (Hoer. c. 13), Praedestinatus (Hoar. c. xii), and the continuator of Tertullian (Pseudo-Tertullian, Hoer. c. xii). St. Epiphanius, in his great work on heresies (Hoer. lib. 30 c. iii), communicates a letter of this Ptolemy to Flora, in which the former explains to the lady the fundamental features of his doctrine. The only difference between the Ptolemaeans and the Valentinians in general appears to have been in respect to the number of aeons which they invented for their respective systems, and the name of Ptolemy is associated particularly with that of Heracleon as regards a duplex system of four. SEE HERACLEONITES. In the year 1843 Mr. Stieren. who has since made himself more generally known by his recently commenced edition of the works of St. Irenaeus, published a dissertation under the title De Ptolemoei Gnostici ad Floram Epistola, etc. (Jenae, ap. C. Hochhausen), in which he endeavors to prove that the doctrine contained in the letter to Flora is at variance with the system of Ptolemy as known by the writings of St. Irenaeus, and that, in consequence, the letter must be considered as apocryphal. Hefele, in the Tubinger Quartalschrift, 1845, p. 387-396, undertook to show that there is no real contradiction between the letter and the sys tem, and that neither the authenticity nor the integrity (except one marginal note in cap. 1, § 6) of the former can be questioned. — Wetzer u. Welte, Kirchen-Lexikon, s.v.