Ace Double #D-277 first printing 1958 paperback; 35 cent cover price. Condition is VG+ to near-Fine: tight and square with flat spine, age-tanning is mild and uniform (decent for its vintage); 1/2" and 1" fold-traces at upper right corner of Wollheim-anthology side; very light overall wear (slight rubbing or loss of gloss.) Call the Leinster side near-Fine and the Wollheim side VG+. No stamps, marks or writing - a very clean copy that looks unread. Excellent shape for an Ace Double over fifty years old.

Ace Double D-277 (1958), containing City on the Moon by Murray Leinster (pseudonym of Will F. Jenkins), and Men on the Moon - an anthology of stories set on the moon, edited by Donald A. Wollheim. This is the first paperback appearance for either.

City on the Moon by Murray Leinster - the Avalon hardcover appeared in 1957. Further progress in atomic power could only come about as a result of experiments so dangerous that they could only be conducted in an isolated space station near the far side of the moon. If successful, these experiments could open the way to the stars… To supply this space lab was the duty of the CITY ON THE MOON. When Joe Kenmore, moon-colonist, realized that there were agents working actively to sabotage the city, he knew he was up against a supreme crisis - one in which his own life and those of his fellow colonists were mere pawns to be sacrificed ruthlessly by that hidden foe - unless he personally could block their deviltry.

This is the third book to feature Joe Kenmore - the other 2 (both from 1953) were Space Platform and Space Tug.

(Bound with) Men on the Moon, a reprint-anthology edited by Donald A. Wollheim. Cover by Ed Emshwiller, 137 pages.

(Introduction by Donald A. Wollheim)
"Operation Pumice" by Raymond Z. Gallun (How we flew to the Moon)
"Jetsam" by A. Bertram Chandler (And how we landed on it)
"The Reluctant Heroes" by Frank M. Robinson (How we settled there)
"Moonwalk" by H. B. Fyfe (What we saw around us)
"Keyhole" by Murray Leinster (The surprise that awaited us)

These originally appeared from 1949 to 1953 in Thrilling Wonder Stories, New Worlds, Galaxy, and Space SF. My favorite from this batch is "Keyhole."