Lampsilis powellii is a rare species of freshwater mussel known by the common name Arkansas fatmucket. It is endemic to Arkansas in the United States, where it occurs in the Ouachita, Saline, and Caddo River systems. It is one of two mussels endemic to Arksansas, the other being speckled pocketbook (Lampsilis streckeri). It is a federally listed threatened species of the United States.