Name:
Archaeocidaris illinoisensis
Age: Mississippian
Formation: St. Louis Formation
Location: St. Louis, Missouri
Size: Plate is 8.6 inches tall
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This is a very rare echinoderm fossil. It is a multiple plate of 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 urchins were found YEARS ago, and just now prepared. These spiny urchins are larger than the Lepidocidaris found in the Mississippian Warsaw Formation, and are OLDER than the Pennsylvanian Archaeocidaris from Texas. There are at least EIGHTEEN urchins preserved on the plate! These echinoids 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 uncommon. The echinoids display well on the large, semi-squared block of matrix that also has other partial urchins preserved. This is an extremely prolific multiple example of Mississippian echinoids from the St. Louis Formation.
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