Aided by falling interest rates in the second quarter, five big banks reported earnings Monday morning. And though four of them met or beat Wall Street's earnings estimates, investors still seemed disappointed.

Let's start with

Dow component

Citigroup

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, the largest U.S. financial services firm. Citigroup's profits totaled $3.79 billion, or 74 cents a share. That's up 14% from the $3.34 billion, or 65 cents a share, the bank earned a year ago. "Citi's earnings were solid, particularly in light of the current conditions," said Henry McVey, an analyst at

Morgan Stanley Dean Witter

. But a cautious forecast for the rest of the year by

Bank of New York

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kept the sector from running giddily into the green. Citigroup, for its part, rose just 29 cents, or 0.6%, to $49.15.

Bank of New York's second-quarter earnings came in at 52 cents a share, increasing 8% from the year-ago period. But investors didn't cotton to the bank's cautious outlook. The bank told investors to expect earnings-per-share growth to remain at the second quarter's level in the second half of the year if the market doesn't improve. With analysts previously expecting earnings to grow 10% and 12% in the year's two remaining quarters, Bank of New York got hit hard, falling $6.40, or 13%, to $43.

Each bank that reported earnings Monday went out of its way in its earnings release to highlight the current difficult market conditions. But only Bank of New York was openly skeptical about the coming quarters' prospects.

Bank of America

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was the only bank besides Citigroup to close in the green Monday, despite being the only bank to report a decline in profits during the second quarter. In that period, Bank of America's earnings-per-share fell 2% from the year ago period. The stock closed up $1.13, or 1.9%, to $61.38.

The mixed sentiment over the banking sector was reflected in the sector indices, weighing slightly more heavily to the downside. The

Philadelphia Stock Exchange/KBW Bank Index

slid 1.2% on the day.

Fifth Third Bank

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reported profits of $338.2 million, or 58 cents a share, in-line with the

Thomson Financial/First Call

consensus estimate, and up from last year's second-quarter profit of $296.7 million, or 46 cents a share. The bank's results were underpinned by increased profit margins on retail lending, which it attributed to falling interest rates. The increase in margins drove its core operating profits 14% higher than they were in the year-ago period. Andrew Collins, banks analyst at

U.S. Bancorp Piper Jaffray,

feels that these widening margins could be a boon for the entire banking sector.

Fifth Third fell $2.42, or 3.9%, to $60.42.

Rounding out this morning's list was

Northern Trust

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, whose second-quarter earnings of 57 cents a share, 7.5% higher than the year-ago period and a penny better than the First Call consensus. Traders sent the stock down $3.55, or 5.5%, to $61.01.