Note: The introduction to this story in the The Ghouls anthology states:

Since the original story is stylistically somewhat pedestrian and long-winded, this special abridgement has been prepared which remains not only faithful to the original, but also emphasizes the drama of the film—a film which in my opinion well merits the claims made for it by Carlos Clarens in his book , An Illustrated History of the Horror Film, that "Consciously or not, the influence of the Phantom of the Opera has been felt in most horror efforts ever since."

There is no credit nor copyright notice stated that documents who abridged the text and when. It's assumed that someone at Stein and Day did this while preparing the original hardcover edition of The Ghouls anthology. It's possible the anthology editor, Peter Haining, did the work.