Thanks,
That was a lucky guess. Something from far distant Classics lessons rang a bell - Scylla was a nymph turned into a monster!
I've just had a look at the list of previous types and I'm afraid to say it's going to take me a considerable amount of time to find something that's not been posted before. What's more, I don't think I've got the right kit with me to upload an image. I'd be grateful if someone else could keep this going while I get my ducks in a row.
PH