help what are they?

in the last few month I've been getting these little white dots all over my glass rocks and even my snails. I have know Idea what they are.
when I scrape them off the glass it leaves a little white ring because the part that was atached to the glass doesn't come off as easy. They seem to have a hard shell and a soft inside. I'm pretty sure there alive, becuase they keep multiplying. They sort of remind me of tiny salt water limpits(I think thats what there called) the little rond snail like things, or barnicals. Is there any freshwater barnical? I've never seen them before and I only have them in one tank.
Heres some pics that should help you out.

Originally posted by Mrditty
I see you have a snail or two in your tank I hope you like them becuse you are going to have a whole lot more.
The white dots are snail eggs

Click to expand...

definatly not snail eggs, I have three kinds of snails, and have seen all of them lay eggs, none of them look like this.
So there is such think as a freachwater limpit, do you have any info on them?