Shares of May Department Stores ( MAY) gained after the closing bell Friday when the company revealed that its chairman and chief executive had resigned. Offering no reasons behind his abrupt departure, the department store operator said its board of directors accepted the resignation from Gene Kahn, "thanking him for his many years of service to May and wishing him well for the future." The company's president, John Dunham, has been named acting chairman and chief executive. He will also tend to his duties as president. May said a search to fill the chief executive position permanently will begin immediately and will include both internal and external candidates. Its board elected Russell E. Palmer as lead director. James M. Kilts, also a director, will chair the search committee. The company's stock was recently up 93 cents, or 3.3%, to $29 in after-hours trading, after adding 0.4% during regular trading hours.