The BSE Sensex which shed over 76 points in opening trade today, fell further by 79 points as funds and retail investors booked gains recorded in the previous three sessions despite a firming trend on other Asian bourses.The 30-share index was down nearly 155 points and was trading at 16,692 during noon .In a similar fashion, the wide-based National Stock Exchange Nifty was down nearly 42 points to around 5,085.