POLYPLACOPHORAN MOLLUSCS OF THE ESSEX FAUNA (MIDDLE PENNSYLVANIAN, ILLINOIS)

Several hundred specimens of Pterochiton concinnus (Richardson) have now been collected from the Mazon Creek area. All are articulated, and most show all eight valves, held in place by a girdle, the margin of which is heavily spiculate. Most specimens preserve the radula, which is remarkably similar to that of living specimens.