Lampsilis cardium is a species of freshwater mussel in the family Unionidae, the river mussels. It is known commonly as the plain pocketbook. It is widespread in eastern North America, where it is native to the Mississippi River and Great Lakes drainage systems.
Shell is thick and usually yellow to tan in color*. Shell is suboval, inflated with prominent beaks. Juveniles have many thick green lines on the outside of the valve that become less apparent as the mussel ages. Pale blueish white nacre. Can grow to a relatively large size (7 inches). Both pseudocardinal and lateral teeth are prominent. **
Males and females show sexual dimorphism. Female more inflated and rounded, with truncated posterior. *
(Source: Freshwater Mussels of the Upper Mississippi)
*(Source: A Field Guide to the Freshwater Mussels of the Chicago Wilderness).
Plain pocketbooks can easily be confused with fatmuckets.
The fatmucket has a more elongated shell with double-looped lines as beak sculpture. **
**(Source: A Field Guide to the Freshwater Mussels of the Chicago Wilderness).
Milwaukee Riverkeeper has found valves fairly commonly in the main branch of the Milwaukee River. Live mussels of this species have also been found.