Platyceras and Acanthocrinus Fossilized Spines

This piece of Devonian Period limestone is from the Jeffersonville layer of Clark County, Indiana. It is unique in that it contains spines from two types of creatures: snail and crinoid. The solid spines are from the Acanthocrinus or Gilbertocrinus while the hollow ones might be from the Platyceras snail.

Thanks to Kenny for the picture.