Mystery Shell

we find some interesting nature specimens in our backyard. Today we found this large snail shell. Not sure if it washes up with a storm, or if the birds eat them and then leave the shells. Skyler was using the "Guide to Seashore Life" book to try and see of we could ID what kind of shell/animal it was.

we think it may be a "Lewis' Moon Snail" at least that was the closest resemblence in the book.