Ptychagnostus atavis Agnostid Trilobites

Order Agnostida comprises trilobites that appeared in the Lower Cambrian, became widespread and then declined to become rare in the Ordovician prior to their complete extinction by the end of the Ordovician. They are so unusual that some experts have suggested that one of the two suborders, Agnostina, should not even be included in Class Trilobita. Believed plantonic, they often lacked eyes, and their cephalon and pygidium are of essentially the same size.

This plate coming from the Middle Cambrian of Millard County, Utah contains 24 specimens of the species Ptychagnostus atavus.