Bumastus niagarensis (Whitfield, 1879) trilobite pygidium fossil found in the Waldron Shale of Clark County, Indiana USA. It dates to the Silurian Period (Wenlock Epoch, Sheinwoodian to Homerian Stages). Species was originally named by R. P. (Robert Parr) Whitfield (1828-1910) as Illaenus niagarensis in the Annual Report of Geological Survey of Wisconsin for 1879, 1880 page 68.
I came across a number of these fossils in my Waldron Shale box while looking for brachiopod fossils to send off to another collector.