What is "thriae"

The Thriae or Thriai were nymphs, three virginal sisters, one of a number of such triads ("maiden trinities" Jane Ellen Harrison called them) in Greek mythology. They received names Melaina ("The Black"), Kleodora ("Famed for her Gift"), and Daphnis ("Laurel"); however, in the page in the Corycian nymphs, the third sister is listed as Corycia. They were the three Naiads ( nymphs) of the sacred springs of the Corycian Cave of Mount Parnassus in Phocis.

Corycia was the sister whom the Corycian Cave was named after. She was the mother of Lycoreus with Apollo.

Kleodora was loved by Poseidon. With Poseidon (or Kleopompos) she was the mother of Parnassos, who founded the city of Parnassus. ( Pausanias 10.6.13).

Melaina was loved by Apollo, bearing him Delphos. Another tradition names Thyia as the mother of Delphos. Her name meant "the black," suggesting she presides over subterranean nymphs.