If Bear Stearns is worth just $236 million this morning, about 90 percent less than what it was worth last week, what's Lehman Brothers' value? Or Merrill Lynch's?

It's the dawn of a new day for shareholders of the biggest Wall Street firms, and it's an ugly one. In a report published this morning, Oppenheimer analyst Meredith Whitney predicted that brokerage stocks could see half their value wiped away.

Indeed, premarket traders sent Lehman shares down nearly 30 percent this morning. Shares of Merrill Lynch, Morgan Stanley, Goldman Sachs, and Citigroup also fell.

The market is particularly concerned about the fate of Lehman Brothers, which said last week it plans to cut about 5 percent of its workforce. This morning, Moody's lowered its ratings outlook on Lehman debt from positive to stable. Credit-default swaps on Lehman, which reflect the cost of protecting the bank's debt, soared this morning.

Lehman was also punished by a rumor that traders at DBS Group, one of the biggest banks in Southeast Asia, had been instructed to avoid transactions with Lehman. A later email went out reversing those instructions, according to the Wall Street Journal.

Investors will find out if the selloff is warranted tomorrow, when Lehman is scheduled to report its first-quarter results.

Morgan Stanley, which has seen its shares fall more than 11 percent in premarket trading, will report earnings on Wednesday.

If there is another shoe to drop among the biggest brokerage firms, investors are rightly concerned that there may not be another white knight like J.P. Morgan. The Federal Reserve can't continue to finance $30 billion bailouts. Sovereign wealth funds were already burned by their foray into these stocks, and aside from J.P. Morgan, there are few possibilities in the private sector that seem likely to step in.

Edward Hadas at Breaking Views is alarmed by the grim outlook. "One path leads to multiple financial bankruptcies, debt deflation, and depression," he writes. "Another leads to the effective nationalization of much of the financial industry, with the risk of runaway inflation."

Also on Portfolio.com:

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• Market Movers: Is Bear Stearns Really Worth $2?
• Market Movers: The Fed Needs Credit Confidence to Return. Today.
• Economics: The Economy of Fear
• Wall Street: It's a Mad, Mad, Mad, Mad World