This is Amazing Stories for September 1940, cover by Robert Fuqua. The ISFDB entry for this issue is here. I found this version of the cover at Pulp Covers, which also provides us with a back cover:

The included text there is something to behold: “Life on Europa (moon of Jupiter). This member of the solar system is only slightly smaller than Earth’s moon. Science knows little about it, and thus, lacking conclusive observation, our artist pictures its life in imaginative style (see page 144 for details).” Sure, why not?

You can read and download the entire issue at the Internet Archive.