Difference between longnose and big long nose butterfly fish?

I was reading the Marine Fishes pocket guide by Scott Michael and in the book it list 2 different butterfly fish. 1 is the yellow longnose butterfly fish and the other is the big longnose butterfly fish? I was wondering if there were any real differences? It sounds like one is basically obsolete to find forcipiger longirostris (big longnose) and the other fairly common. Anyone have any additional info on this?