Various is the correct author for any book with multiple unknown authors, and is acceptable for books with multiple known authors, especially if not all are known or the list is very long (over 50).
If an editor is known, however, Various is not necessary. List the name of the editor as the primary author (with role "editor"). Contributing authors' names follow it.
Note: WorldCat is an excellent resource for finding author information and contents of anthologies.
Entretenidísima antología de relatos que recogen la historia de España desde la extinción de los Neanderthales hasta los descubrimientos arqueológicos de los años veinte del siglo pasado. Relatos excepcionalmente documentados que dan una visión muy interesante de la Historia.