Wikipedia
Bakevelliidae
Bakevelliidae is an extinct family of prehistoric bivalves that lived from the Late Mississippian until the Middle Eocene. Bakevelliidae species are found worldwide, excluding Antarctica. Living a stationary life attached to substrate in marine and brackish environments, they formed shells of an aragonite composition with a low amount of magnesium calcite. The family was named by King in 1850. At least one genus in the family, Hoernesia, has a notably twisted commissure join.