Euproops danae
Pennsylvanian
Francis Creek Shale
Pit 11, Will Co.
Illinois, USA.

Euproops danae is important scientifically because it demonstrates the long evolutionary stability of horseshoe crab body plans. Modern horseshoe crabs retain many features already present in their Carboniferous relatives more than 300 million years ago
37mm horseshoe crab including telson in 68mm paired concretion.