(Θριαί) the name of three prophetic nymphs on Mount Parnassus, by whom Apollo was reared, and who were believed to have invented the art of prophecy by means of little stones (θριαί), which were thrown into an urn. (Hom. Hymn. in Merc. 552 ; Schol. ad Callim. Hymn. in Apoll. 45 ; comp. Lobeck, Aglaoph. p. 814.)
[L.S]A Dictionary of Greek and Roman biography and mythology
Smith, William
A Dictionary of Greek and Roman biography and mythology. William Smith, LLD, ed. 1890