Fast snails with almost invisible shells are usually Stomatellas, but it's impossible to tell from your pic. Try photographing it in a dish of water, and back off until you can get your camera to focus. A small in-focus pic is better than a larger blurry one. You should then be able to crop out a lot of the background leaving a decently large pic of the snail. Try that, I think I can give you a positive ID if you do.
Cheers,
Don