At the Penn Dixie site, near Blasdell NY, it is very common to find Phacops rana trilobites and sometimes Greenops sp. trilobites. One of the more rare trilboites to be found there is Dipleura and when you do find them it's often just isolated pieces. Such is the case with the specimen below of a pygidium from a Dipleura dekayi. The fossil is very smooth despite all the dots that you can see on the surface. I'm used to finding specimens of D. dekayi in my local Mahantango formation that don't have any shell material left and the dots are preserved as small columns. This indicates that they served some purpose in life, perhaps as sensory organs?
This specimen was found in the Bay View Coral Bed in the Windom Shale of the Moscow Formation (Devonian, Givetian stage).