Galaxy Magabook No. 3 by Theodore Sturgeon, 1963, cover art by Gray Morrow
Baby is Three: “The boy went to the psychiatrist because he needed help—but his problem was something no analyst could handle. He knew his name—but not his identity. He knew what he did—but not what he was. Worst of all, he didn’t know how many of him there were.”
. . . And My Fear is Great: “The fear that lurked inside him was a demon that drove him to desperate measures of hatred and terror. It promised him all the riches of the earth. It carried him to a God- like power—until it met an even more frightful monster outside!”
Galaxy Magabook No. 2: After Worlds End & The Legon of Time
by Jack Williamson, 1963, cover art by Ed Emshwiller
After Worlds End: “In this strange world danger was his every day companion—despair dogged his steps—and the greatest peril of all was his only hope for life!”
The Legion of Time: “They stormed the wall of the future on the trail of one woman who was too evil to live—and another who might never be born at all!”
Galaxy Books/Publishing was once a bustling enterprise. The Galaxy Novel series, ran for 31 editions as digest-sized paperbacks. Then there were four more (#32–35) produced in the standard paperback-size of the day, aka 1958. A year later, Beacon Books continued the series with eleven more editions in paperback-size that extended the series through 1961.
And finally, in 1963, a short-lived series of three digest-sized book/magazines appeared. Dubbed a “Magabook” each edition included two compete novels. The first was The Sky is Falling and Badge of Infamy, both by Lester Del Rey, with cover artwork by Virgil Finlay.
See indexes at Internet Speculative Fiction Database and Galactic Central.
Both series of digest-sized novels are covered in depth by Steve Carper and Gary Lovisi in TDE4.