Definitely Cerith eggs. Fortunately, Cerith snails, when the eggs hatch, are a snail. A lot of snails start out as a planktonic critter and metamorph to a snail a few weeks later. Because of this, our skimmers usually suck them up and they don't survive.
Make sure your calcium levels are high. The babies really need this to develop their shells.
I think I gave you the wrong information. Cerith snails do indeed go through a larval period, in which they are part of the planktonic soup. So, you'd need an aquarium with no filtration, and a source of phytoplankton, in which they can feed on.
Sorry about that.