Arthroacantha carpenteri CRINOID Devonian Arkona Fm. Arkona, Ontario, Canada Size: 6.7 cm cown It is rare to obtain crinoid crowns from the Arkona Fm. The rock is NOT water proof and so any rain completely destroys any visible specimens. Crowns can only be obtained by excavation and even that is difficult. Price: $350 US ID number: d1023