This excerpt taken from the NDAQ 8-K filed Feb 20, 2008.
Conversion of class A common stock
On January 20, 2007, the third anniversary of the demutualization of the Exchange, all 46,900 shares of Class A Common Stock converted to Class B Common Stock such that all 441,504 shares of the Exchange are, as of that date, Class B shares. Upon conversion to Class B, the eligibility of holders of Class A shares for a contingent dividend, terminated. The former holders of the Class A shares otherwise continue to have the same rights and privileges, including voting, as the Class B holders.
Philadelphia Stock Exchange, Inc.