Hardy boys mystery stories / Franklin W Dixon

1. 

   Book 44

   The Masked Monkey

   Leslie McFarlane

2. 

   Mystery of the Desert Giant

   Leslie McFarlane

3. 

   Mystery of the Whale Tattoo (Hardy Boys)

   Leslie McFarlane

4. 

   The Arctic Patrol Mystery

   Leslie McFarlane

Book data and covers from Open Library (openlibrary.org).