Small calcareous plates, possibly from Asteroidea or other Echinodermata, occur in the Maquoketa shale of Iowa. These plates all have similar characteristics, but vary in their minute structures, and the variations apparently have some stratigraphic significance.
Proceedings of the Iowa Academy of Science
©1939 Iowa Academy of Science, Inc.
Spivey, R. C.
"Occurrence of Certain Small Fossil Plates in the Maquoketa Shale of Iowa,"
Proceedings of the Iowa Academy of Science, 46(1), 251-251.
Available at: https://scholarworks.uni.edu/pias/vol46/iss1/61