Good Cheer (thaleia)
THALEIA was a Naiad-nymph of Mount Aitna (Etna) in Sicily. She was loved by the god Zeus but, fearing the wrath of Hera, asked to be hidden beneath the earth. There she gave birth to the Palikoi (Palici)--twin Sicilian gods of hot springs and geysers.
HEPHAISTOS (Stephanus Byzantium?)
THALEIA (Thaleia). A daughter of Hephaestus, and by Zeus, the mother of the Palici. (Serv. ad Aen. ix. 584; Steph. Byz. s. v. palikê.) The Palikoi were Sicilian daemons, twin sons of Zeus and the Nymph Thaleia, the daughter of Hephaestus. Thaleia, from her fear of Hera, desired to be swallowed up by the earth; this was done, but in due time she sent forth from the earth twin boys, who were called Palikoi, from tou palin ikesthai.
Source: Dictionary of Greek and Roman Biography and Mythology.
CLASSICAL LITERATURE QUOTES
Aeschylus, Women of Aetna (lost play) (Greek tragedy C5th B.C.) :
Aeschylus' lost tragedy the Women of Aetna or Aetnaeae told the story of Thaleia, mother of the Sicilian Palikoi (Palici). The plot is summarized by Smyth (L.C.L) : "A Sicilian maiden named Thaleia or Aitna (Aetna), having been embraced by Zeus, in fear of Hera's wrath prayed that the earth might open and swallow her up. Her prayer was granted, but when the time of her delivery was at hand, the earth opened again and twin boys came forth, who were called Palïkoi, because they had ‘come back’ (apo tou palin hikesthai) from the earth."
The history of the play's composition is outlined in the ancient work Life of Aeschylus : "Having arrived in Sicily, as Hiero was then (476 B.C.) founding the city of Aetna, Aeschylus exhibited his Aetnae as an augury of a prosperous life for those who were uniting in the settlement of the city."
- Aeschylus, Fragments - Greek Tragedy C5th B.C.
Other references not currently quoted here: Macrobius Saturnalia 5.19.15, Stephanus Byzantium s.v. Palike.