(Scale bar is 1 cm.)The specific name of this sand dollar translates from Latin as "Chinese hat", in reference to the low conical shape of the shell in cross section. It is by far the most common fossil sand dollar in Georgia, often occurring in vast numbers at a single locality.
Periarchus pileussinensis is only found in the lower and middle part of the Ocala Limestone in Georgia. Care should be taken to distinguish it from Periarchus lyelli, occasionally known from the middle Eocene and the lowest part of the upper Eocene. P. lyelli has a much lower, more rounded upper surface and generally a thicker edge than P. pileussinensis.
As with most sand dollars, the species's shell suggests a preference for sandy sediment, but this one is also found in finer grained sediments than might be predicted.
AGE: LATE EOCENE
FORMATION: OCALA LIMESTONE
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