Well your snails must be happy! Congrats! BTW, there's nothing wrong with being ecstatic over snails. My roommates thought I was crazy when I found a huge bristleworm one time and was all happy about it.
Do you know for sure that's a cerith? I have what I THOUGHT were cerith (maybe nerite?) snails that reproduce like nuts, and the young survive. The eggs are different though, they're larger, round, and clear laid in a straight line. I found approx. 100 or so in my 30 gallon tank, and I started with 6. They graze the glass day and night. There is a close up pic of two copulating in "My 6 gallon Tank" link.