Notes: Info from Amazon.com. Illustrated by Frank R. Paul is stated on title page. As it is unclear if all the original illustrations from the Wonder Stories Quarterly, Spring 1931 serialization (in one part) had been reprinted, a single entry is added here. If someone with access to the two publications can compare images, that single entry may need to be replaced with the multiple interior art images from the magazine record. Cover artist based on visual match with the first Avon edition of the novel.