Law360 says a Manhattan federal judge has been trying to assess the size of a potential class action alleging that a dozen megabanks, including Goldman Sachs Group and Bank of America, colluded to block start-up trading platforms from entering the giant market for interest rate swaps. The plaintiffs'-side lawyer alluded to potential billion-dollar damages. "The pecuniary back-and-forth punctuated a 3 1/2-hour oral argument session before US District Judge Paul Engelmayer in a ceremonial Manhattan courtroom full with some 50 dark-suited corporate lawyers," the legal news website Law360 reports.