(Πετόσιρις), an Egyptian priest and astrologer, who is generally named along with Nechepsos, an Egyptian king. The two are said to be the founders of astrology, and of the art of casting nativities. Suidas (s. v.) states that Petosiris wrote on the right mode of worshipping the gods, astrological mas ἐκ τῶν ίερῶν βιβλίων (which are often referred to in connection with astrology), and a work on the Egyptian mysteries. But we may infer from a statement made by Vettins Valens, of which the substance is given by Marlsham (Canon Chronicus, p. 479, ed. Lips. 1676), that Suidas assigns to Petosiris, what others attribute partly to him, and partly to Nechepsos. For his , or, Ψῆφος σεληνιακὴ, containing astrological principles for predictinul the event of diseases, and for his other writings, Fabricius ( Bibl. Graec. vol. iv. may be consulted. And to the list given by him may be added a translation into Latin by Bede, of the astrological letter of Petosiris to Nechepsos, entitled, De Divinalione Morlis et Vitae. (Bed. Opera, vol. ii. pp. 233, 234, ed. Col. Agripp. 1612.) His name, as connected with astrology, was in high repute early in Greece, and in Rome, in her degenerate days. This we learn from the praises bestowed on him by Manethon (5.10), who, indeed, in the prologue to the first and fifth books of his professes only to expand in Greek verse the prose rules of Petosiris; from Julius Firnicus (Mathes. iv. in praefat. &c.), who calls Petosiris and Nechepsos, diuini illi uiri utque omni admiratiose diyai ; and, from the refece of Pliny. H. N. 1.23, 7.49.) But the best proof is the fact, that, like our own Lilly, Petosiris becamlle the commonto namlsfe for an astrologer, as we find in Aristophanes, quoted by Athenaells (iii. p. 114c.), in the 46th epigram of Lucillius (Jacobs, Anthol. Graec vol. iii. p. 38), whence we learn the quantity, and in Juvenal, 6.580. Marsham has a full dissertation on Nechepsos and Petosiris, in the work above quoted (pp. 474-481).