I don't think it's a sundial either. You can pick it up & check it's front door, or whatever it's called. It's fairly distinctive on a sundial. In Ophuira's photo (see Viper's reply) you can visualize it fairly well.
Thanks for all the replies. After I posted this last night I went to get the little guy out and take a closer look a couldn't find it.
Bonebrake:
Yes they are my zoos.
Bob
It doesn't really look like it to me, just a common hitchhiker snail. If you found him again look at the portion of the shell that closes the snail in. If its pointed then its a sundial.