mystery snails are either male or female, unlike ramshorns which are hermaphrodites and exchange sperm. you may have had two of the same sex. if you want to try again, i would suggest getting three or four of them. i've had several losses, though, and it's taken 4 or 5 months to finally get eggs. i thought that they just like to escape, but my theory now is that the ones that got out, got lost, and died were actually all females. they lay their eggs in large obvious peach-colored clutches above the waterline, and i think they were looking for a surface to lay on when they fell out of the tank. make sure that there aren't any openings. mine finally laid eggs on the inside of the lid. the one i have left has two new partners now, a black one and a very small albino, and he mates with them as if he has five minutes left to live.