(Author Surname page number)
Note: The medium is the type of electronic file (i.e. Kindle file, Nook file, EPUB file, PDF file). For example, if the book was read on an electronic device like a Nook, Kindle your citation would look like this:
Rowley, Hazel. Franklin and Eleanor: An Extraordinary Marriage. New York: Farrar, 2010. Kindle file.
More info on citing e-books here. You can also refer to section 5.7.18 in the MLA manual.