Are "shelled nuts" with or without their shells?
In cooking, "shelled" usually means "de-shelled" or "shell-less". This applies to nuts, peas, etc. 

The opposite that I've seen most often is "shell" to indicate that they still have their shell. 

"Shell peanuts" have their shell intact.
"Shelled peanuts" are just the meat that has been removed from the shell