Pictures of two marble size cystoids (Rhombifera) of the Waldron Shale (Niagara Limestone) of Clark County, Indiana. These cystoids are called Holocystites sp. and existed in the Silurian Period. See another one in the database of the Indiana State Museum. Caryocrinites persculptis cystoids have also been found in the Waldron Shale as seen at this website.
These are the first cystoids I have ever found. Learn more about these amazing creatures at the entry of Wikipedia.
