The Sensex at the Bombay Stock Exchange plunged by 344 points to 26,475 in early trade today. In the last trading session on Friday, the 30-share index had plummeted 699 points to an over 4-month closing low.At the forex market, the rupee was trading lower by 42 paise at 67 rupees 67 paise against the dollar in opening trade today. On Friday, the rupee had lost 62 paise to end at over three-month low of 67 rupees 25 paise.