FILE PHOTO: A Citibank sign on a bank branch in midtown Manhattan, New York, November 17, 2010. REUTERS/Mike Segar/File Photo

NEW YORK (Reuters) - A unit of Citigroup Inc has shut down one of its private stock trading venues, often referred to as dark pools, as part of a broader review of the bank’s equities business, the bank said on Monday.

Citigroup Global Markets’ CitiCross alternative trading system (ATS) ceased operations on April 30, according to a filing from the U.S. Securities and Exchange Commission.

“We have decided to shut down the CitiCross ATS as part of a strategic review of our equities business. We continue to invest in talent and technology to drive wallet share growth in global equities,” Citi spokesman Scott Helfman said in a statement.

Last month Citi reported a 24 percent drop in equities trading revenue in the first quarter due in part to lower market volumes, pressuring the bank’s overall revenue.

Nearly 25 million shares were matched in CitiCross during the week of April 15, placing it 23rd out of 32 active U.S. ATSs in terms of size, according to the most recent statistics from the Financial Industry Regulatory Authority. The average trade size was under 200 shares.

Dark pools are electronic broker-run trading venues, and every big bank has one. They allow investors to trade shares without the trading data becoming available until after the trades happen, reducing the chance that others in the market will catch wind of the buyer’s or seller’s intentions and move the price against them.

The private trading venues have traditionally been more lightly regulated than public stock exchanges like those run by Nasdaq Inc and New York Stock Exchange-owner Intercontinental Exchange Inc, but in recent years regulatory scrutiny and compliance costs have increased.

Citi still operates a block trading ATS called CitiBLOC, according to the SEC filing. That ATS matched just over 6.4 million shares with an average trade size of more than 15,000 shares in the week of April 15, according to FINRA.