Arthroacantha carpenteri Devonian Arkona Formation Arkona, Ontario, Canada One of the nicest specimens of this crinoid from this locality. Crinoids from this locality are very difficult to obtain due to the nature of the shale. The shale turn to mud with the slightest rainfall. Special techniques are required to remove complete crinoids at this locality. Size: 14.5 cm including stem. This specimen was donated to the University of Michigan for permanent display in the new museum.