Knight Capital Group said its volume of trading in U.S. equities fell 19.3% in December, compared to November. Its volume also fell 3.5% from a year earlier.

Average daily volume was $22.1 billion. That compared to $27.4 billion in November 2011 and $22.9 billion in December 2010.

Transactions fell to 3.5 million a day, from 4.1 million in November. But the number was up from 3.2 million in December a year ago.

Knight said its earnings in the fourth quarter, however, quadrupled from a year ago.

The group reported earnings of $40.2 million or 43 cents a share for the last three months of 2011.

That compared to $9.2 million and 10 cents a share in the last quarter of 2010.

Revenues from continuing operations for the fourth quarter of 2011 were $341.3 million, compared to $259.0 million from continuing operations for the fourth quarter of 2010.

" Market Making performed exceptionally well and again demonstrated the ability to adapt to the trading environment and deliver results. While the fourth quarter was not without its challenges, the contribution from Electronic Execution Services increased and we worked to improve profitability across products and services," said Thomas M. Joyce, Chairman and Chief Executive Officer, Knight Capital Group.

"Continuing operations" includes the company's Market Making, Institutional Sales and Trading, Electronic Execution Services, and Corporate and Other segments.

Market Making consists of all global market making across equities, fixed income, foreign exchange and options as well as the company's activities as a Designated Market Maker at the NYSE.

Institutional Sales and Trading includes full-service institutional research, sales and trading as well as equity and debt capital markets, reverse mortgage origination and securitization, and asset management.

Electronic Execution Services includes Knight Direct, Hotspot FX and Knight BondPoint.

Corporate and Other includes strategic investments primarily in financial services-related ventures, clearing and settlement activity, corporate overhead expenses and all other income and expenses that are not attributable to the other reporting segments.

Tom Steinert-Threlkeld writes for Securities Technology Monitor.