The complete trilogy as originally published in the 1930's:
Kaldar, World of Antares
A stupendous novelette of a world far removed from Earth, of the Chan of Kaldar, and the spider-people from beyond the metal mountains
The Snake-Men of Kaldar
Another mighty tale of Kaldar, world of Antares--a tale of red warfare against a race of monsters on a distant planet
The Great Brain of Kaldar
A superb tale of distant Kaldar, world of the great star Antares