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.

This mussel, a bivalve mollusc in family Unionidae, is oblong oval in shape and can reach over 10 centimeters in length.

The shell is brownish to olive green to tawny in color on the outside and iridescent bluish white on the inner surface.

In a cyst on the fish they undergo metamorphosis to become juvenile mussels and then drop to the substrate to develop further.