Thanks msj, I found that link in another thread.
I just can't tell from those photos, because I never see the snail from that angle, and I'd prefer not to pull it out of the tank if possible.
Okay, so you can see the curled up antenna, and the, and the oval structure to the left of that (which is speckled, I think) - that is what I thought might be the penis sheath. So what is it?
Why not just pick the snail out and make it come out of the shell enough for you to see if it has a penis or not? The link posted by Rachel is excellent.