If it's the item I'm thinking of, it's called a shirt front. Sort of like a waist-length dickey that's been starched to death. There were removable collars and cuffs, too. You'd change the collar and cuffs (and shirt front) every day, instead of the whole shirt, thus reducing the size of your laundry bill. Some of them were washable (starched linen) and some were disposable. I'd guess Mr Field's was one of the then-cutting-edge celluloid ones, which were advertised as guaranteed not to go limp no matter how hot or damp it got.