From the Fort Payne Chert (Mississippian) of northern Alabama, here's what I think to be an Archimedes bryozoan in cross section. Scale is in centimeters.
Am I correct? Can you suggest a more specific identification? I was unfortunately unable to collect this one, as it was in a fairly large rock, but I know where to find it next time. Thanks in advance for your consideration.
EDIT: I was wrong, this is from the Monteagle Limestone (also Mississippian).