Strobilocystites polleyi is the first cystoid that I have from the Devonian. I won it from an auction on E-bay and it fits in well with my collection of fossils from the Cedar Valley Formation of Iowa.
It is composed of many large plates with a single Aulacophore present about 3/4 up the side of the body. Cystoids are odd echinoderms that I don't understand very well so I may have the terminology of the anatomy incorrect.
This specimen came with a label that states it came from the Cedar Valley Formation (Devonian, Givetian) near Palo, Iowa. I found an old excerpt called "Echinoderms of the Iowa Devonian" by A. O. Thomas that discuss' this species and others found in Iowa. I'm not sure what publication it was part of originally.