For eBooks from an online library, such as ebrary, include the DOI or home page URL.
Burns, M. (2007). About Teaching Mathematics: A K-8 Resource (3rd ed.). Retrieved from http://site.ebrary.com/
For eBooks downloaded to a physical device, e.g., Kindle, Sony Reader, or Nook include the e-reader version in square brackets. Include the DOI or if there isn’t one, the site the eBook was downloaded from.
Gladwell, M. (2008). Outliers: The story of success [Kindle DX version]. Retrieved from http://www.amazon.com/
Brill, P. (2004). The winner’s way [Adobe Digital Editions version]. doi:10.1036/007142363X
(American Psychological Association, 2010, p. 203)