To continue discussion on the specimen listed here, with renewed focus on it being a Cephalopod.
As of right now, I'm deciding between Solenocheilus and Ephippioceras.
Going directly by the book: Index Fossils of North America (1944, 1980 printing), I can see positives for both.
Solenocheilus
(Lower Mississippian to Lower Permian, IN, IL, MO, KS, TX and Europe)
Recommended by a local expert, but doesn't specialize in Cephalopods.
Ephippioceras
(Mississippian in Europe, Pennsylvanian, Ohio to Kentucky, Nebraska to Texas)
The raised line along the midline of the plate photo is what is selling me on this one. My specimen is much larger than the plate, but not quite double the size.
So, two new photos of the specimen.
First, looking at the line:
(After seeing it this way, I was looking at it 90 degrees in the wrong direction)
Flipped, End over end.
So, any opinions? I was thinking of removing more matrix from the matrix heavy size, but it will certainly remove the shell material and leave the steinkern.