LISBON, Portugal (AP) — Shares in troubled Portuguese bank Banco Espirito Santo have plunged by more than 50 percent in volatile early trading on the Lisbon stock exchange a day after it reported a record half-year loss of 3.58 billion euros ($4.8 billion). The fall began after an audit discovered accounting irregularities at the bank's parent company and gathered momentum after three of the Espirito Santo family's holding companies requested bankruptcy protection.