Crinoid

Melocrinus clarkei

• Devonian
• West River Shale, Genesee Formation
• Canandaigua Lake, New York, USA

Size: 11 cm across the arms

Melocrinus is a striking crinoid genus with arms unlike any other. The inner free arms in each ray are fused into a thick biserial "trunk", from which uniserial arms branch off exotomously every few plates, and these arms themselves bear pinnules. Also characteristic is a very wide interradial area. Calyx ornamentation is highly-variable among species, and M. clarkei is characterized by very subtle, delicate ridges that appear to ripple across the plates.