A second seat on the New York Stock Exchange (search) sold Friday, but the price fell to $2.5 million, down $100,000 from a sale made earlier in the day.

The latest transaction marked the first decline in seat prices since the Big Board announced plans to merge with electronic trading exchange Archipelago Holdings (AX).

Before today, seat prices have climbed steadily since the deal was made public on April 20. Earlier a seat sold for $2.6 million, up $200,000 from the previous sale, just shy of the record seat price of $2.7 million reached in August 1999.

The value of an exchange seat has more than doubled since touching a 9-year low of $975,000 in early January. The decline was driven by uncertainty over the NYSE's business prospects amid the increasing popularity of electronic trading.

The 212-year-old Big Board is known for its open outcry auction system and floor trading, which some have criticized for being slow and outdated.

The Archipelago deal, however, diminished the uncertainty surrounding the NYSE's future.

According to the terms of the deal, the NYSE's 1,366 seat holders will share a $400 million cash payout and get 70 percent of the stock in a publicly traded Big Board.

Financier Kenneth Langone (search) has launched a bid to acquire the exchange with a consortium of investors to counter the Archipelago deal.

Shares of Archipelago were up nearly 7 percent to $31.75.