eBooks are often "hidden" as they are linked to the indexed master print edition. Click the links icon on any book and all the ISBN numbers for the linked books can be seen. Click the ISBN you own and click +Bookshelf to add it to your Bookshelf.
An alternative way to add any books (print or digital) that you cannot find in the Library is to import the ISBN numbers. The Import Books page is linked from the My Bookshelf tab. If the book is already in the Library it gets added to your Bookshelf immediately. If not, we will try to retrieve the data from Amazon. In the case of eBooks this may not work since Amazon only lists Kindle editions. If your eBooks are not Kindle, email us the ISBN numbers and we will add them for you.