What a pretty cup and saucer!
Actually it is a plate with a saucer-type indentation, so you can hold you cake and your cup. I don't know what they are called, and bought it at a second hand store. I love old china: just wish I could put it in the dishwasher.
Yes, I see now that the cup is off center and the plate is too big to be saucer. Maybe you can find more-- how cool to have a set or even several in different patterns. I like old china too-- I hope I find one sometime!