This fossil is a Strophodonta brachiopod from the Potter's Farm formation near Alpena, Michigan. I've looked through the book "Strata and Megafossils of the Middle Devonian Silica Formation" and I believe this can be classified as Strophodonta crassa. The radial ribs are much coarser compared to the typical Strophodonta demissa and the shell is thinner.
Here is another specimen that is just the pedicle valve
The Potters Farm formation is part of the Traverse Group of rocks in Michigan. They are dated to the upper Givetian stage of the middle Devonian. I received both of these specimens from a member of the Fossil Forum but I don't remember his member name.
Some specimens of Strophodonta crassa are pictured on the Friends of the University of Michigan Museum of Paleontology's web site Here.