Mumbai, Aug 4 - A key index of the Indian equities markets was trading on a volatile note Tuesday, though in a tightly bound range, and was ruling 111 points in the red about 90 minutes before closing bell.

Around 2.06 p.m., the 30-scrip sensitive index (Sensex) of the Bombay Stock Exchange (BSE), which opened at 15,940.1 points, was ruling 110.78 points or 0.7 percent down at 15,813.45 points.

The Nifty of the National Stock Exchange (NSE), too, was ruling in the red at 4,670.6 points, down 0.87 percent.

Broader market indices were mixed with the BSE midcap index slipping into the negative terrain under selling pressure and was ruling 0.27 percent lower.

At the same time, the BSE small cap index still managed to hold onto its slender gains and was up 0.36 percent.