Megastrophia are very large shells and when one gets an intact specimen you are lucky. I had some luck on my side when I uncovered the Megastrophia below at the Penn Dixie site near Blasdell, New York. I took extra care to excavate the rock around it so that it wouldn't break apart as I extracted it. As it is I soaked it in a thin solution of Elmer's glue and water to help strengthen the fossil.
I'm not sure if both valves are present with this fossil as it is so delicate I don't want to work on it. It was collected from the Windom Shale member of the Moscow formation which is middle Devonian (Givetian) in age.