A quick post that is non Ordovician. I am uncertain of the chronology of the changes to geologic time, but in the mid 19th century the Silurian was comprised of the lower Paleozoic periods that are recognized today as the Cambrian, Ordovician, and the Silurian.
So, just a quick post to show a nice little proetid that I found in Jefferson Co. Kentucky. It was found in the Mid. Silurian rocks near the disconformity with the over-laying Jeffersonville Limestone. I am uncertain of the id, but it is probably a Crassiproetus.