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 Fig ?*&** kind 



g 



to the Cystideans, Pentremites, and ( ^ 

 Marsupites. In America, a genus of 

 fossils called Agelacrinus 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 

 (Ophiura). Evidently these two types have been in 

 existence throughout all the silent revolutions, phy- 

 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." 



