Possible Clues:

• Six-headed creature colleague Lewis picked up?
• Monster opposite Charybdis
• Lake circled by horrible scaly monster
• Monster with Charybdis
• Sea monster
• Monstrous female, noted Liverpudlian you say?
• Greek sea monster who devoured sailors
• Sea monster in Greek mythology
• Sea monster devouring sailors trying to escape from Charybdis
• In Greek mythology, a female sea monster