Today, while cleaning my flowerbed (removing dead leaves, pulling some weeds, etc) I happened to notice a rock with an intriguing imprint that appeared to be a spiral. I immediately thought of a fossil and I'm pretty sure I'm right since rocks usually don't have 'faces' like this. The fossil is about 3cm at it's largest point and looks like either an ammonite or some sore of bivalve to me, but I'm not a palentologist by any measure, so I'd like some clearer IDing if possible. Thanks!
(ps. If the fossil isn't clear enough, especially the spiral, I found that the contrast improves drastically with a quick rinse, so let me know if you can see it well enough.)