The French stock exchange opened down again Tuesday, led by plunging bank shares, with highstreet giants BNP Paribas down three percent and Societe Generale down four. The CAC40 index as a whole was down 0.75 percent on 2,918.07, but all eyes were on the banks, following overnight reports that German engineering firm Siemens had withdrawn half-a-billion euros from a French lender.