A few specimens of Strophodonta demissa from the Windom Shale (Bay View Coral Bed) as found at the Penn Dixie Site near Blasdell, NY. These are smaller than the specimen I found along Lake Erie and those from Sylvania, OH, but are about the size of those I've found at Arkona.
Specimen #1 (wet because I'd just washed off some light mud)
Specimen #2 (this one is completely dry)
The Windom shale is part of the Moscow Formation which is middle Deovnian (Givetian stage) in age.