* The name is misspelled: Check if you've got the correct spelling.
* He's a lesser-known author: It's possible he's written books but hasn't achieved widespread fame. You might be able to find information on smaller online book databases or local libraries.
* He's an author who uses a pen name: He might write under a different name, and you're searching for the wrong one.
Could you provide more context about this author? For example:
* What kind of books does he write? (Genre, subject matter, etc.)
* Do you know any specific titles he's written?
* Where did you encounter this name? (A book review, library catalog, etc.)
With more information, I might be able to help you track down Herbert Samuel Mallory's work.