Harlequin PANs from the 1950's
Between 1953 and 1958 Harlequin Books of Toronto Canada published several titles in association with PAN Books of London

The Four Just Men The Secret Of Chimneys
Number 349 from1956 Number 377 from 1957
  
The Lost World The Great Impersonation The India-Rubber Men
Number 238 from 1953 Number 221 from 1953 Number 352 from 1956
 
The Square Emerald Dark Bahama The Secret Adversary
Number 334 from1955 Number 354 from1956 Number 359 from1956
       
The Man In The Brown Suit The Clue Of The Silver Key The Ringer
Number 337 from1955 Number 361from1956 Number 378 from1957