Most cephalopod specimens I find are small to medium in size. They range from 3-5 inches in diameter. This one was much larger. Found as a huge slab of limestone in the middle of Guffy Run, recent storms brought this rock to rest in the center of the stream. It looks like water erosion helped expose the Cephalopod. I originally thought I had a clam, but as it dried a septum line revealed itself.
Upon getting more opinions, this could also be a Sea Pen or even an Oyster.
Removed from matrix
Piece removed from larger specimen 
Piece removed from larger specimen