My original tumblr post was here. This February 1942 cover for Famous Fantastic Mysteries contains the text “Complete Novel in this Issue: Radio Planet and the Ant Men, by Ralph Milne Farley.” It was first posted by pulpcovers.com.
Tumblr favorite #2284: WTF is that thing i?
The cover is by Virgil Finlay:
https://rashmanly.files.wordpress.com/2010/11/famous_fantastic_mysteries_apr_1942_virgil_finlay_cover_m1.jpg