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Name:
Archaeocidaris illinoisensis
Age: Mississippian
Formation: St. Louis Formation
Location: St. Louis, Missouri
Size: Plate is 3.3 inches tall
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This is a very nice echinoderm fossil. It is a plate of two Archaeocidaris illinoisensis from the Mississippian of St. Louis. Fossil echinoids from the St. Louis area are famous around the world and have been extremely sought-after by collectors for decades. These spiny urchins are LARGER than the Lepidocidaris found in the Mississippian Warsaw Formation, and are OLDER than the Pennsylvanian Archaeocidaris from Texas. These two urchins themselves are complete with MANY barbed spines still intact. Most of the types of urchins from this site have smooth spines (there are three species!), and ones with the barbed spines are rare. The echinoids display well on the large, natural plate of matrix that also has urchin remains scattered about. This is a very nice example of two Mississippian echinoids from the St. Louis Formation.
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