Crinoid Cross Section?

[FedEx]

Found in a creek in South Mississippi. I thought it was a crinoid stem split in half when I first found it, but after looking at some google images, it doesn’t look like a crinoid cross section to me. Maybe it’s the internal chambers of a nautiloid? The formation is middle Miocene. I mostly find coral and crinoids in the area. There are also some other fossil bits sticking out of the matrix that I photographed as well.