Brian Earl Brown posted this list in the comments, and I decided to move it up here to make it easier for people who might be looking for this information to find it. Thanks, Brian!I've read more than half of these novels and will probably get around to all of them sooner or later.
1.The Torture Trust, Secret Agent X , Feb., 1934 (v1-1) Written by Paul Chadwick)
2. The Spectral Stranglers, Secret Agent X , Mar., 1934(v1-2) Written by Paul Chadwick
3. The Death-Torch Terrors, Secret Agent X , Apr., 1934 (v1-3) Written by Paul Chadwick
4. The Ambassador of Doom, Secret Agent X , May, 1934 (v2-1) Written by Paul Chadwick
5. City of the Living Dead, Secret Agent X , June, 1934(v2-2) Written by Paul Chadwick
6. Hand of Horror, Secret Agent X , Aug., 1934(v2-3) Written by Emile C Tepperman
7. Octopus of Crime, Secret Agent X , Sept., 1934 (v3-1) Written by Paul Chadwick
8. The Hooded Hordes, Secret Agent X , Oct., 1934(v3-2) Written by Paul Chadwick
9. Servants of the Skull, Secret Agent X , Nov., 1934 (v3-3) Written by Emile C Tepperman
10. The Murder Monster, Secret Agent X , Dec., 1934 (v4-1) Written by Emile C Tepperman
11. The Sinister Scourge, Secret Agent X , Jan., 1935 (v4-2) Written by Paul Chadwick
12. Curse of the Waiting Death, Secret Agent X , Feb., 1935 (v4-3) Written by Paul Chadwick
13. Devils of Darkness, Secret Agent X , Mar., 1935 (v5-1) Written by Paul Chadwick
14. Talons of Terror, Secret Agent X , Apr., 1935 (v5-2) Written by Emile C Tepperman
15. The Corpse Cavalcade, Secret Agent X , May, 1935(v5-3) Written by G. T. Fleming-Roberts
16. The Golden Ghoul, Secret Agent X , July, 1935 (v6-1) Written by G. T. Fleming-Roberts
17. The Monarch of Murder, Secret Agent X , Aug., 1935(v6-2) Written by Paul Chadwick
18. Legion of the Living Dead, Secret Agent X , Sept., 1935(v6-3) Written by Paul Chadwick
19. Horde of the Damned, Secret Agent X , Oct., 1935(v7-1) Written by Paul Chadwick
20. Ringmaster of Doom, Secret Agent X , Nov., 1935 (v7-2) Written by G. T. Fleming-Roberts
21. Kingdom of Blue Corpses, Secret Agent X , Dec., 1935(v7-3) Written by Unknown
22. Brand of the Metal Maiden, Secret Agent X , Jan., 1936 (V7-4) Written by G. T. Fleming-Roberts
23. Dividends of Doom, Secret Agent X , Feb., 1936 (v8-1) Written by G. T. Fleming-Roberts
24. The Fear Merchants, Secret Agent X , Mar., 1936 (v8-2) Written by Paul Chadwick
25. The Faceless Fury, Secret Agent X , Apr., 1936 (v8-3) Written by G. T. Fleming-Roberts
26. Subterranean Scourge, Secret Agent X , June, 1936(v8-4) Written by G. T. Fleming-Roberts
27. The Doom Director, Secret Agent X , Aug., 1936 (v9-1) Written by G. T. Fleming-Roberts
28. City of Madness, Secret Agent X , Oct., 1936 (v9-2) Written by G. T. Fleming-Roberts
29. Horror's Handclasp, Secret Agent X , Dec., 1936(9-3) Written by G. T. Fleming-Roberts
30. Death's Frozen Formula, Secret Agent X , Feb., 1937(v9-4) Written by G. T. Fleming-Roberts
31. The Murder Brain, Secret Agent X , Apr., 1937 (v11-1) Written by G. T. Fleming-Roberts
32. Slaves of the Scorpion, Secret Agent X , June, 1937 (v11-2) Written by G. T. Fleming-Roberts
33. Satan's Syndicate, Secret Agent X , Aug., 1937 (v11-3) Written by G. T. Fleming-Roberts
34. The Assassin's League, Secret Agent X , Oct., 1937 (v11-4) Written by G. T. Fleming-Roberts
35. Plague of the Golden Death, Secret Agent X , Dec., 1937 (v12-1) Written by G. T. Fleming-Roberts
36. Curse of the Mandarin's Fan, Secret Agent X , Feb., 1938 (v12-2) Written by G. T. Fleming-Roberts
37. Claws of the Corpse Cult, Secret Agent X , Apr., 1938 (v12-3) Written by G. T. Fleming-Roberts
38. The Corpse That Murdered, Secret Agent X , June, 1938(v12-4) Written by G. T. Fleming-Roberts
39. Curse of the Crimson Horde, Secret Agent X , Sept, 1938 (v13-1) Written by Paul Chadwick
40. Corpse Contraband, Secret Agent X , Dec., 1938 (v123-2) Written by G. T. Fleming-Roberts
41. Yoke of the Crimson Coterie, Secret Agent X , Mar., 1939(v13-3) Written by G. T. Fleming-Roberts
