Compared to the last Clypeaster that I featured on my blog, Clypeaster rogersi is much much smaller. It still has the typical features of the genera, namely a central mound shape in the center on the top (adapical) surface and an overall round shape to the test (exoskeleton). The size is not determinative of the species as there are specimens in the 7cm range known from Georgia.
Adapical (top) surface
Adoral (bottom or underside)
This specimen comes from the early Oligocene (Rupelian stage) aged Mariana formation of Mississippi.
Here is a general write up of the species and how to differentiate it from another common species found in the same aged rocks.
This site has an official description of the species including some typical occurrence areas in the US, Cuba and Mexico.