White Spots on my glass?

[snake1]

For awhile now actually years now I have always had these white shell like crustaceans grow on my overflow or glass when not cleaned for awhile. I cleaned my glass about 4 weeks ago and my glass is covered again they are like a shell toughness and feel, you have to scrape with credit card or razor. I finally found a jewelers eye piece and looked at these spots up close on the glass they look like egg sacks each one looks about the same size and white color but inside each one has a different amount of what looks like yellow eggs does anyone know what these are and if they are bad or good....I`m leaning towards snail eggs I have Nerite, Turbo, Trouchs , Nassarius, and Cerith sorry if spelled incorrectly I cant find anything online that shows what I`m looking at .... Thanks for you help in advance I will try to get better Pictures if needed>

 

[degibson84]

When I added nwtites to my last system I had these all over my rock work. I believe that's whose eggs they are

 

[Postal]

+1 on nerite eggs.
I actually used to have them lay eggs on astrea snails.

 

[snake1]

thanks to the two of you that's what they look like and I think your right....whats the likely hood they will hatch and become more snails