Echinoid spines and plates

These pictures are of pieces of the echinoid Archaeocidaris from the Mississippian Period. They were found in the St. Benevieve Formation of Hardin County.

Thanks to Pam for the fossils.

This first picture shows two echinoid plates from an inside view.

Here is an overall view of the plates and spines of the echinoid with a metric ruler.

 

Spines of the echinoid, Archaeocidaris found in Kentucky.

 

Echinoid plates that spines were attached to.