Ceyx, son of Eosphorus (In Roman mythology, Ceyx was the daughter of Lucifer) and the king of Thessaly was married to Alcyone in Greek mythology. They were very happy together, but then Ceyx perished in a shipwreck and Alcyone threw herself into the sea. Out of compassion, the gods changed them into the halcyon birds. Since Alcyone made her nest on the beach, and waves threatened to destroy it, Aeolus restrained his winds and made the waves be calm during seven days in each year, so she could lay her eggs. These became known as the "halcyon days", when storms never occur. The halcyon became a symbol of tranquillity. (Ovid XI, 410).
Ceyx is a genus of kingfisher, as is Halcyon.