• http://en.wikipedia.org/wiki/Crinoid
  
  
• http://www.uky.edu/KGS/coal/webfossl/pages/crinoid.html
  
  
• http://animaldiversity.ummz.umich.edu/site/accounts/information/Crinoidea.html
  
  
• http://palaeo-electronica.org/education/states.htm