With Wall Street still reeling from the NYSE’s planned merger with Archipelago Holdings Inc., the Nasdaq Stock Market Inc. has now entered into a definitive agreement to acquire Instinet Group Inc.

As part of the deal for Instinet, Nasdaq has entered into a definitive agreement to sell Instinet’s institutional brokerage division to Silver Lake Partners, leaving Nasdaq with the trading system. Instinet has also entered into a definitive agreement to sell its Lynch, Jones & Ryan subsidiary to Bank of New York prior to consummation of the Nasdaq transaction.

Instinet stockholders will receive approximately US$1.9 billion in cash, comprised of approximately US$934.5 million from Nasdaq, approximately US$207.5 million from Silver Lake and the balance from INET’s available cash, including approximately US$174 million from Bank of New York.

In a news release, Nasdaq says the combination of Nasdaq with the INET ECN, “will provide all investors with a technologically superior trading platform that is positioned to compete effectively in a post-Regulation NMS environment.” Nasdaq also says it expects to realize significant savings with the help of the INET technology. It expects the transaction to reduce clearing costs and corporate expenses associated with the combined entity. And, it anticipates this transaction will be accretive to its shareholders within 12 months of closing.

Bob Greifeld, president and CEO of Nasdaq, commented, “This transaction will allow Nasdaq to compete more effectively with other U.S. and international market centers by making our technological platform more competitive, which will result in greater cost efficiencies and improved quality of execution in our market — qualities that today’s individual and institutional investors demand. Nasdaq will continue to innovate and will also have the ability to tap new opportunities in other asset classes.”

To finance the transaction, Nasdaq has obtained commitments for: US$750 million in 6-year senior term debt, with JPMorgan and Merrill Lynch acting as joint lead arrangers and joint bookrunners; US$205 million in convertible notes to Hellman & Friedman LLC and Silver Lake Partners. Hellman & Friedman has also restructured the terms of Nasdaq’s existing US$240 million convertible notes, extending the maturity date to 2012, lowering the interest coupon rate to 3.75% from 4%, and lowering the notes’ conversion price to US$14.50 from US$20.00.

Patrick Healy, managing director of Hellman & Friedman and a Nasdaq board member, stated, “As Nasdaq’s largest shareholder, Hellman & Friedman is pleased to support Bob Greifeld and the Nasdaq management team in the acquisition of INET. We believe this transaction will allow Nasdaq to further optimize and enhance its electronic trading environment to benefit all investors, while maintaining its status as the low cost provider.”

Nasdaq’s board of directors has approved the deal. And, Reuters, which owns approximately 62% of Instinet Group, has agreed to vote its shares in Nasdaq in favor of the transaction. Nasdaq’s purchase of Instinet is subject to customary closing conditions and regulatory approval, including approval by Instinet shareholders.

Thomas Weisel Partners LLC acted as exclusive financial advisor to Nasdaq. Skadden, Arps, Slate, Meagher & Flom LLP was Nasdaq’s outside legal counsel, and Keefe, Bruyette & Woods, Inc. rendered a fairness opinion to the Nasdaq Board of Directors with respect to the convertible notes issued by Nasdaq.