ST. PETERSBURG, Fla. – Four credit unions, including two billion-dollar CUs, have extended their agreements with PSCU Financial Services' PayLynx online bill pay service. They are $1.7 billion DFCU Financial of Dearborn, Mich.; $562 million Lockheed Georgia Employees' FCU of Marietta; $124 million U.S. First FCU of San Mateo, Calif., and $2.8 billion Vystar CU of Jacksonville, Fla. PayLynx subscribers also now number more than 200,000, the CUSO said. PSCU Financial Services now offers single sign-on interfaces to more than 16 Internet home banking vendors, with others under development or consideration, the organization says.