At the moment when you reach the final page of shelf view there is no "Previous" button. Unlike previous pages in the "Want to Read" or "Read" section that weren't the first 40 entries. Having a "Previous" button on this final page would be nice for when users want to go back to the previous entries. Especially if they were linked to the page, in which case they can't even go back in their browser unless they know how to edit the URL properly.