In Greek mythology, Themisto (; ) was the daughter of the river god InachusClement, Recognitions 10.21 and the mother of Arcas by ZeusPseudo-Clement, Recognitions 10, p. 123, l. 40; she was transformed into a bear by Hera.Eustathius ad Homer, Iliad p. 300; Stephanus of Byzantium, s.v. Arcadia (Ἀρκαδία)
In other accounts, the usual birth mother of Arcas was called Callisto, daughter of Lycaon or else Megisto, daughter of Ceteus,Hyginus, 2.1.6, and 2.6.2, with Araethus of Tegea as authority both women were members of the Arcadian royal family.
Notes
References Pseudo-Clement, Recognitions from Ante-Nicene Library Volume 8, translated by Smith, Rev. Thomas. T. & T. Clark, Edinburgh. 1867. Online version at theio.com Stephanus of Byzantium, Stephani Byzantii Ethnicorum quae supersunt, edited by August Meineike (1790–1870), published 1849. A few entries from this important ancient handbook of place names have been translated by Brady Kiesling. Online version at the Topos Text Project.