The Dolphins signed S Gerald Alexander and placed WR Roberto Wallace on injured reserve, the team announced Wednesday.
Alexander, a fourth-year veteran, has played in 41 games, with 30 starts, and has tallied 14 passes defensed, four interceptions, three forced fumbles and two sacks. The 6-2, 209-pound Boise State product has spent time with the Panthers (2010), Jaguars (2009-10) and Lions (2007-08). He had signed with the Dolphins on Aug. 29 but was cut on Sept. 3.
Wallace, who has been hampered with a quadriceps injury, hadn't played since Week Two and did not record a reception this season.