Here is a Devonian period clam found in the Silver Creek formation. This formation can be found in Clark County, Indiana. The clam is known as Paracyclas elliptica.
The Smithsonian has a collection for a geologist named Nettleroth and they have some reports I found on-line. I think they are from the mid to late 1800s when a lot of the fossils in the Louisville area were named. Nettleroth refers to the Silver Creek formation as "hydraulic limestone". Also he refers to Clark County as Clarke County. I have also seen Speed, Indiana referred to as Speeds, Indiana in older texts.
UPDATE: This entry has been modified with a picture of another clam fossil. As of August 2010, this fossil was on display at the Smithsonian Museum of Natural History. It list it was found in Kentucky.