Pleurobema sintoxia
Pleurobema sintoxia, the round pigtoe, is a species of freshwater mussel, an aquatic bivalve mollusk in the family Unionidae, the river mussels. Distribution and conservation status 
This species is native to eastern North America. It is found in the drainages of the Ohio River, the St. Lawrence River, and the Great Lakes. The Canadian Species at Risk Act listed it in the List of Wildlife Species at Risk as being endangered in Canada. References

Bivalves of North America
Molluscs of Canada
Fauna of the Great Lakes region (North America)
sintoxia