Nautiloid?

I found this shell today, making a trip to southern Washington County, Arkansas. Near the community of Winslow, and Devil's Den St. Park, I followed a dirt road and found some exposed rock in a ditch.

Cracking one open, I found fossils. This was excitation for me, because there is almost 700 feet in elevation difference from Benton county. I'm talking different geological era! Big stuff, friends. Different species of fauna, etc. For a landlocked fossil enthusiast, that much of a change in elevation means traveling to a foreign country, so to speak. Ed. note: this appears to be in the vicinity of the Bloyd shale formation. The Bloyd shale is primarily sandstone, secondarily shale. Its time period is middle Pennsylvanian

Here's the shell, still in its matrix.