Mew is a black-backed gull in Roverandom. Mew lives on a cliff-face (suggested by Hammond and Scull to be somewhere near Filey:97) and is the postman for the sand-sorcerer Psamathos Psamathides.:26
In the story, Mew takes Rover to the moon at the request of Psamathos; they fly via Mew's cliff-edge home, over the Isle of Dogs and see the seas flowing over the edges of the world.:20 Whilst at the moon, Mew continues to deliver post to the Man-in-the-Moon before - once Roverandom's adventures on the moon are finished - taking Rover (now known as Roverandom) back to Psamathos.:55
"mew" is a term used to describe the noise by a cat or a gull.