This smooth, round snail like fossil is actually a cephalopod called a Gonaitite from the Moscow formation (Devonian, Givetian stage) that I found at a quarry off Deep Springs Rd. in Madison County, NY. They were precursors to ammonites and evolved from primitive bactritid type nautiloids. This specimen is a good size but does not preserve the sutures which would help to identify it. Tornoceras sp. is the most common genera in the Moscow formation and this could be a specimen of one. You can't see it in the pictures but there are a couple of thin cracks in the fossil that are filled with golden pyrite. It shows best when the rock is wet.