How to cite a google book?

If a student comes to the desk asking: How do I cite a book found from Google book search? Do we have a definite answer? It seems not. You could say: "you cite it as the electronic equivalent". I would think so too, but just not so sure about it. So can you tell if the following examples from Wikipedia are correct ways to cite (APA):

Ballard, Joe N. (1998). Horatio Wright. In The History of the U.S. Army Corps of Engineers. DIANE Publishing. p. 143. ISBN 0-7881-7666-8. Google Book Search. Retrieved on December 23, 2007.

Nash, Jay Robert (1994). Encyclopedia of Western Lawmen & Outlaws. Da Capo Press. p. 250. ISBN 030680591X. Amazon Books. Retrieved on April 13, 2005.