I doubt that anybody will be able to give you a 100% guarantee. What other snails do you have in the tank? They are reminiscent of Cerith snail eggs- but really hard to tell. I thought that Nas. eggs were more of a single pack; but then I recalled this picture of an Nas. laying eggs-
http://i93.photobucket.com/albums/l5...segglaying.jpg so it would appear that I could be wrong. As eggs it is really hard to tell one snail from another... Being as you have a photo with the Nas in it I would put money on it being Nas eggs (not much $$, mind you...)
Good luck.