Goodreads Librarians Group discussion

I have a problem deciding on what constitutes a 'subtitle' when listing the title of some books. Using this book as an example:

http://www.goodreads.com/book/show/15...

The title is 'There Are Giants in the Sea', which is then followed by 'Monsters and Mysteries of the Depths Explored'. This second line of text is used on the front cover only - not on the spine and not anywhere else inside the book.

Should it be listed as a subtitle, or not?

I would leave it as a subtitle, since it is listed on the front cover of the book.

Subtitles don't often fit on a book's spine, and not sure why it isn't inside the book, but we usually make determinations based on the front cover (often we don't have access to the physical book.)