Publisher:Lancer

A selection of 1961-70s Lancer covers are available at bookscans.com.

"Lancer Science Fiction Library" may be a publisher/publication series worth noting. E.g. Notes in indicate there may have been two such series.

Lancer Science Fiction Library 1st Series 1962-65
Confirmed:
 * 72-758 Edmund Cooper
 * 72-768 L. Sprague de Camp
 * 72-721 Edmond Hamilton
 * 72-942 Eric Frank Russell
 * 73-421 Jack Williamson
 * 73-441 Dean McLaughlin
 * 74-807 Jack Vance
 * 74-810 Robert Silverberg
 * 74-811 John Christopher
 * 74-812 Jack Williamson
 * 74-815 Isaac Asimov
 * 74-816 Isaac Asimov
 * 74-819 Eric Frank Russell

Suspected:
 * 74-808 Stanley G. Weinbaum
 * 74-818 Isaac Asimov

Second series
Confirmed:
 * 447-75385-095 Hal Clement
 * 447-75464-095 Henry Kuttner

Suspected:
 * 447-75422-095 Hal Clement