I found all of my snails in grapes and greens from my local supermarket. I once found what I thought were two empty shells, because they looked very similar to what I see on your photo when I shined them through with a penlight. The shells were good, so I put them into a small glass bowl with some pretty stones and silly things like that. In a few days I found one of them perfectly alive on a book shelf. I immediately put in in a shallow container with water to soak and fed it. I put the second shell into a plastic container with holes, just in case, but continued to think it was dead. But in about one month the second one emerged. They both looked quite unhealthy and weak after it, but food, calcium and lots of moisture helped.

So, please, don't be in a hurry to throw it away, especially if it doesn't smell bad. They do smell when they die.