NEW YORK ( TheStreet) -- Sirius XM Radio ( SIRI - Get Report) and E*Trade Financial ( ETFC - Get Report) both saw a rise in short interest in the second half of May, according to Nasdaq data published by Reuters. Sirius saw short interest increase to nearly 215 million shares, up from 209 million in the previous half of May, making it the most heavily shorted stock on the Nasdaq for at least the second straight period since TheStreet began tracking the data. E*Trade was number four on the list of most heavily shorted stocks, with 86 million shares sold short, up from 83 million in the period ending May 14. LVLT), with 112 shares sold short, YRC Worldwide ( YRCW - Get Report) with 98 million in short interest and Myland Inc ( MYL - Get Report) with 82 million in short interest. In total, short interest in Nasdaq stocks swelled to 7.21 billion in the last half of May from 7.18 billion in the first half of the month. The shares held short equate to roughly 2.69 days of average daily volume for the Nasdaq, compared with an average of 2.34 days for the previous reporting period, the exchange operator said. -- Written by Dan Freed in New York.