The Chaldean sea-god. It had a fish's head and body, and also a human head; a fish's tail, and also feet under the tail and fish's head. In the day-time he lived with men to instruct them in the arts and sciences, but at night retired to the ocean. Anedotes or Idotion was a similar deity, so was the Dagon [dag-On, fish On] of the Philistines.
Source: Dictionary of Phrase and Fable, E. Cobham Brewer, 1894