Transferring EPUBs from iBooks for iOS to iBooks for Mac OS X

Over the last couple of years I have saved dozens of documents to iBooks for iOS (I'm on iOS 9.3.1). Some were web pages I had Safari for iOS convert into PDFs and then open in iBooks on iOS. Others were EPUBs I downloaded from Project Gutenberg, using Safari on iOS to do the downloading.

Now I want to read all these books and PDFs on iBooks on Mac OS X (10.11.4).

However, when I open iBooks on Mac OS X, all I see are the books that I had downloaded from iTunes to iBooks on iOS. I cannot see any of the dozens of EPUBs and PDFs that I downloaded to or created on iOS.

Thinking that there might be a way to "share" books from iBooks on iOS, I went to the "Mail" function, hoping that I could attach a book from iBooks on iOS to an email, mail it to myself, and open it up on my Mac with iBooks. No luck. All that happens is that it creates an email with the title of the EPUB or PDF, but it does not attach the book itself to the email.

Am I asking for a feature that does not exist?

What sort of workarounds might be available?