Procambarus pentastylus, a new crayfish of the subgenus Pennides, is described from the Calcasieu River drainage of southwestern Louisiana. The species formerly was confused with Procambarus dupratzi Penn, 1953 but differs in several details of the form I male pleopod, including shorter terminal elements and the presence of a large adventitious process (here termed the pentastyle) mesial to the central projection. Procambarus dupratzi as here restricted is known only from the Sabine, Neches, and Trinity River drainages in Louisiana and Texas. A key to form I males of Pennides species known from west of the Mississippi River is presented.