FOSSIL STAR-FISHES AND SEA-URCHINS. 131 



two different orders, in some measure come as near 

 to the Encrinite family on one side, as the Pouch 

 Encrinite {Marsupites) of the Chalk formation does 

 both to them and the Echini on ^^^ 

 the other. The Cushion-stars (Goni- 

 asters) run very near to the Cake- 

 urchins or Clypeasters, although the 

 former are star-fishes and the latter 

 sea-urchins, and perhaps both these 

 touch as nearly as any of their class „. x- .• . 1 • ^ 



•^ -^ I'lg. 107.— Extinct kind 



to the Cystideans, Pentremites, and (,,:L«Xv.?SrO. 

 Marsupites. In America, a genus of ^'^"^ ^^"^''^ ^'^"^'^• 

 fossils called Agclacrinus connects Star-fishes with the 

 Cystideans. 



Both star-fishes and sea-urchins are, geologically 

 speaking, very ancient marine animals. With the 

 exception of certain Brachiopoda, no other groups of 

 animals have maintained their peculiar shapes for a 

 longer time than the star-fishes. As far back as the 

 Cambrian period we find two well-differentiated orders 

 in existence, one represented by our modern " five- 

 fingers " ( Uraster) and the other by the brittle-stars 

 {OpJunra), Evidently] these two types have been in 

 existence throughout all the silent revolutions, phy-r 

 sical and biological, which have taken place on the 

 surface of the globe ; and our modern star-fishes are 

 as lineal and directly uninterrupted descendants of 

 these early Cambrian fossil forms, as mankind from 

 their " first parents." 



