Cover and interior illustrations are by Gino D’Achille. Unfortunately, I have no scans of the latter. The cover above is from a first edition, while the back sleeve is from a 1985 edition. The book follows the format established by John Keel’s Strange Creatures from Time and Space (Fawcett, 1970). See below for that cover: yet another stunner from Frank Frazetta.
(Back cover image via Library of the Phantasmagoria)