R.H. Donnelley ( RHD) agreed to buy Dex Media ( DEX) in a deal valued at $4.2 billion, creating one of the nation's biggest publishers of directories. Each Dex share will be exchanged for $12.30 in cash and 0.24154 Donnelley shares. Donnelley will also assume Dex's debt, which will probably be around $5.3 billion at the end of the year. Dex shares ended Friday at $27.79, and Donnelley last closed at $63.26. Based on Donnelley's most recent closing price, the pact values Dex at around $27.58 a share. The combined company will be the third-largest print and Internet directory publisher in the U.S. with revenue that would amount to around $2.7 billion a year on a pro forma basis. The company will have more than 600 directories with a total circulation of 73 million. After the merger closes, Dex shareholders will own about 53% of the combined company. The new firm will use the R.H. Donnelley name and be based in Cary, N.C.