Crassiproetus arietinus

As far as I can tell this is a Crassiproetus arietinus from the Little Cedar Formation of Johnson County, Iowa. I say "as far as I can tell" because the trilobites from this formation are not very well documented and C. arietinus is the closest match I could make based on a line drawing and written description. The remarks after the written description state: "Specimens from this interval have been assigned doubtfully to C. arietinus. The holotype is a fragmentary but complete specimen in which the glabell and pygidium have been exfoliated. Since these two features are critical in identifying different species of Crassiproetus, it will be impossible to assign any material to this species with certainty."-- ("Geologic Reconnaissance of the Coralville Lake Area" Orrin Plocher, 1989)