Shares of Citigroup (NYSE: C) are down sharply after the nation's third-largest bank by assets reported disappointing fourth-quarter results. The bank's earnings per share of $0.38 missed the consensus estimate of $0.51.

Looking at the income statement alone, the quarter didn't pan out well for the bank. It reported net income for the fourth quarter of $1.2 billion on revenues of $17.2 billion. This compares with net income of $1.3 billion for the fourth quarter of 2010 on revenues of $18.4 billion, declines of 11% and 7%, respectively.

The full-year results are slightly more nuanced. The bank recorded total net income for 2011 of $11.3 billion compared with $10.6 billion from a year ago, an increase of 6%. Alternatively, its full-year revenue came in at $78.4 billion, down 10% from $86.6 billion in 2010.

From a balance-sheet perspective, both the lending giant's quarter and year look much better. Its tier 1 common ratio, an important measure of a bank's financial strength from a regulator's point of view, increased by more than a full percentage point from the fourth quarter of 2010, going from 10.75% then to 11.8% now. And the bank's tangible book value per share, a core measure of value, came in at $49.81 dollars, an increase of 12% from $44.55 in 2010.

Comparing Citigroup's performance to JPMorgan Chase's (NYSE: JPM) results from last week, the story for banks this earnings season appears split between commercial banking and trading operations. While overall loans were up at both banks -- Citigroup's rose 14% for the quarter and JPMorgan's grew 4% -- the fear emanating from Europe continued to weigh on trading desks.

Next up in terms of earnings is Bank of America (NYSE: BAC), which reports later this week. It'll be important to see whether its commercial banking operations are able to post growth, too.

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