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Found this specimen all by itself, neatly embedded in the surface of the limestone-bedded creek that runs alongside Big Canyon Road to the south of the White Mound site in southern Oklahoma. Geological maps confirm the site is Hunton Group, the same formation group as White Mound, although this matrix is much harder and more crystalline than the limestone at White Mound. This group ranges in age from Early Silurian to Early Devonian. The whole specimen was extracted along with some of the matrix. You might also notice the fossil looks like it's been somewhat dissolved. This is one of the very first fossils that I found and I made the rookie mistake of soaking it in vinegar, thinking it would clean up nicely. Instead it mostly dissolved away the smooth surface features, but the overall structure was preserved. The original state of the fossil (which I should have taken a picture of) was much the same, but less bumpy. I won't be making that mistake again. The tube has multi-layered walls with symmetric rings. It might be hard to see in the photo but the inner walls also have rings. The closest thing I can find in the Audubon book which is the right age is tentaculites. Their picture doesn't really match (their example is much more conical shaped with larger ringlets) but the description is pretty close (except for the "coarse" rings and the width) and the age is appropriate. Here's what they have to say about tentaculites: Description: "60 mm long, 44 mm wide. Small, narrow, straight cone, with coarse rings more uniform toward apex. Area between rings usually has concentric ringlets or lines. Inner wall of cone also has rings. Walls thick, multi-layered, pierced by tiny radiating canals. Interior toward apex has slightly concave septa sealing off sections of tube. Apex closed and bluntly pointed." They also add: "The apex ends either in a point or a small bulb." Age: "Lower Silurian through Upper Devonian (possibly also in the Lower Ordovician)"