Egg sacks on my glass? ID please
 

I have these little "egg sack" things on the glass of my tank.

The first picture is a pic of the glass, you can see they seem to be " placed " in order on the glass.

The second is a picture I took using my sons "eyeclops" they look like little eggs.

The only thing in my tank when these first appeared were Cerith snails, blue hermits and Nassanus snails.

Any idea what they could be?

bump*