Citigroup and JP Morgan, America's two biggest banks, were pressured again over allegations they had helped collapsed energy trader Enron portray loans as income and then tried to market the bookkeeping technique to other companies. Citigroup shares, down 11% on Monday, dived another $5.04 or 16% to $27. JP Morgan lost $4.44 or 18% to $20.08. The allegations, denied by the banks, are under investigation.