Is my snail dead?

I was netting debris from my pond, and I scooped up a large, almost
golfball sized snail. I picked it up to return but when I did, a hard
membrane fell off of the opening and the body of the snail fell out,
it was only about 3/4 of an inch long. And in the shell there were
what looked like eggs. I put the "body" back in and put the shell in
the water, but now is its just floating. Does anyone know what is
going on here? Oh, and by the way, what do they eat and how many
should I keep in a 50 gallon pond.

Thanks,
Gary.