A story yesterday incorrectly stated Rep. Constance A. Morella's vote on impeachment charges against President Clinton. Morella (R-Md.) voted against impeachment.

The ancient Mayan civilization included parts of what is now Mexico, Guatemala, Belize, Honduras and El Salvador. An article in yesterday's Style section described its boundaries incorrectly.

The day of the U.S. Open semifinal match between Martina Hingis and Venus Williams was incorrect in a story in some editions yesterday. The match is Friday.

Because of an error in the Bloomberg News database, a chart with the Washington Investing column in Monday's Washington Business section overstated the three-year return to shareholders of Diagnon Corp. Adjusted for a one-for-six reverse stock split, Diagnon shares were up 21 percent.

An article Sunday about U.S. missile defense plans improperly identified Chas. W. Freeman Jr., a former U.S. ambassador and former assistant secretary of defense. Freeman is chairman of a company that negotiates on behalf of clients, primarily American, around the world to obtain market access and arrange joint ventures and acquisitions. His firm does not represent any Chinese companies and does not accept government contracts or clients. Also, the first name of Swedish Ambassador Rolf Ekeus was misspelled.

An article Friday about merit pay for teachers and principals stated incorrectly that no Washington area school district gives performance bonuses to teachers. Starting this school year, D.C. teachers will receive extra raises if they meet a set of performance goals, a plan that was approved in July by the D.C. financial control board.

CLARIFICATION

An upcoming exhibit at the National Postal Museum, "Posted Aboard R.M.S. Titanic," is scheduled to open Sept. 17 and to run through next June 12. The exhibit dates were omitted from yesterday's calendar listing in Horizon.