or IOLAS (Ἰόλλας, Ἰόλαος, orἸόλας), a writer on materia medica, born in Bithynia, who was probably a contemporary of Heracleides of Tarentum, or a little anterior to him, in the third century B. C., as he is mentioned in company with him by Dioscorides. (De Mat. Med. i. Praef. vol. i. p. 2.) He is mentioned also by Celsus (De Medic. 5.22, p. 93), Pliny (Plin. Nat. 20.73, 76), Galen (De Antid. 1.2, vol. xiv. p. 7), St. Epiphanius (Adv. Haeres. 1.1. 3. p. 3.), and the scholiast on Nicander (Ther. 5.683), but nothing is known of the events of his life, nor are any of his writings preserved.