Here are Tuesday’s biggest percentage gainers and losers in midday trading, along with top volume leaders, among companies with a market cap between $50 million and $750 million:

Biggest percentage gainers:

• R.H. Donnelley Corp. (NYSE:RHD), up 22.4% to $5.95 after the Cary, N.C.-based Yellow Pages publisher after competitor Idearc posted first-quarter earnings above Wall Street expectations. R.H. Donnelley releases earnings on May 8.
• Innophos Holdings, Inc. (Nasdaq:IPHS), up 21.2% to $22.08 after the phosphate producer reported late Monday that it swung to a first-quarter profit of $9.3 million, or $0.43 per share, versus a loss of $2.1 million a year earlier. Wall Street analysts, on average, expected earnings of $0.23 per share.
• China Technology Development Group Corp. (Nasdaq:CTDC), up 19.3% to $5.55 despite no significant news.

Biggest percentage losers:

• Obagi Medical Products, Inc. (Nasdaq:OMPI), down 21% to $6.94 after the Long Beach, Calif.-based skin care products maker missed first-quarter earnings expectations by $0.05 per share.
• Interline Brands, Inc. (NYSE:IBI), down 16.5% to $16.30 after the Jacksonville, Fla.-based distributor of maintenance, repair and operations products said it projects second-quarter earnings in the range of $0.30 to $0.35 a share, and full-year 2008 earnings of $1.45 to $1.61 a share. Wall Street analysts expect a second-quarter profit of $0.40 per share and a full-year profit of $1.65 per share.
• Atlantic Tele-Network, Inc. (Nasdaq:ATNI), down 14.9% to $28.19 after the Salem, Mass.-based provider of telecommunications services in the Caribbean and North America reported first-quarter revenue of $45.6 million, which missed analysts’ expectation of $47.1 million. Quarterly profit came in at $7.9 million, or $0.51 per share, versus Wall Street’s anticipation of $0.56 per share.

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