I can't tell from your pics what kind of snails those are. I have an apple snail and don't know much about other kinds of snails.
Since they are laying eggs under water, I can say that they are not pomecea bridgesii (one of they types of apple snails). Though I think the pomecea canaliculata do, but they grow to be huge, like softballs. So I don't think that's what you've got either.
Try wandering over to http://www.applesnail.net
. Under the discussion forums there are sections on identifying snails. That might help. There is also a section on other snails, which might have pictures.