Sundial snails are baddies along with the clam eating snails. I think theyre trochus snails or something. Bumblebee snails are also known to be predatory towards other snails.
How large is it? Its hard to tell, but it almost looks to me like an oyster drill, which is predatory and quite damaging to oysters...not likely though that you would get a temperate water snail in a reef tank. Come to think of it, many years ago I found a snail just like that on a new piece of rock. I managed to identify it, and it turned out to be a bad one...so I tossed it. However, that was so many years ago that I can't remember anything about the snail other than its appearance.