Despite the Widder formation being roughly equivalent to the Silica Shale of Ohio and Michigan, Strophodonta is an uncommon fossil to find. When found they are often much smaller as well. Below is a specimen I found in July on a visit to Arkona. It's still embedded in the matrix and I'm hesitant to try and break it out for fear of shattering the fossil.
Strophodonta demissa is known from the Hungry Hollow member of the Widder formation from whence this fossil came. I know that this is not a Douvillina inaequistriata because the ribs that decorate the surface are more numerous and thicker.
Here are some Strophodonta from the Silica Shale that I blogged about before.