BOSTON ( TheStreet) -- Ambac Financial ( ABK) was one of several stocks trading below $5 and moving on above-average volume Tuesday after the bond insurer said it is pursuing a prepackaged bankruptcy.Ambac Financial said in a filing with the Securities and Exchange Commission that it is "currently pursuing raising additional capital and is also pursuing a restructuring of its outstanding debt through a prepackaged bankruptcy proceeding." In a previous regulatory filing, Ambac said it may consider a prepackaged bankruptcy or would may seek bankruptcy protection without coming to an agreement with creditors over a reorganization plan. The announcement came as Ambac said it had a second-quarter oss of $57.6 million, or 20 cents a share, narrowing from a year-ago loss of $2.37 billion, or $8.24 a share. Shares of Ambac Financial plunged by 18.8 cents, or 20.8%, to 71.5 cents. Volume topped 23.82 million shares, compared to the average daily share volume of 11.94 million. Elsewhere, SciClone Pharmaceuticals ( SCLN) tumbled by $1.14, or 32.5%, to $2.37 after the company said that the SEC has initiated a formal, non-public investigation. In addition, theDepartment of Justice has requested a meeting with the company regarding its compliance with the Foreign Corrupt Practices Act (FCPA). SciClone said it intends to fully cooperate with the SEC and the DOJ in these matter. The SEC probe announcement came as SciClone posted a second-quarter profit of 11 cents a share, down from 16 cents a share in the year-ago quarter. The company forecasted full-year earnings of 31 cents to 35 cents a share, below the Thomson Reuters average estimate of 36 cents a share. Trading volume topped 1.18 million shares, compared to the average daily share volume of 280,000. Penwest Pharmaceuticals ( PPCO) shares jumped by 24 cents, or 5.2%, to $4.97 after Endo Pharmaceuticals ( ENDP) will acquire all outstanding shares of Penwest for $5 per share in a $144 million cash deal. The transaction will be completed in September, the companies said. Volume topped 2.62 million shares, compared to the average daily share volume of 279,000. Almaden Minerals ( AAU) rallied by 28 cents, or 24.3%, to $1.43 after the mineral exploration company announced results from the first drilling on the Ixtaca zone within the company's Tuligtic project in Puebla State, Mexico. Almaden said the first drilled hole intersected multiple quartz-carbonate-sulphide vein zones over its entire length, which Almaden Chairman J.D. Poliquin called "an exciting new gold-silver prospect in a brand new district." Volume topped 1.02 million shares, compared to the average daily share volume of 89,000. -- Written by Robert Holmes in Boston. Check out all of Tuesday's high-volume, under-$5 stocks at the Dollar Store. View the Dollar Store portfolio on StockPickr. Follow Robert Holmes on Twitter and become a fan of TheStreet.com on Facebook.