INTER-RELATIONS OF ORDERS 



623 



The final result, then, of all our inquiries leads us to a view 

 of the mutual affinities of the classes of Echinoderms, which may 

 be indicated in the following table :— 



Protocoelomata 



I 

 First fixed ancestor 



Asteroidea 



Protopelmatozoa (Thecoidea ?) 



OphiuToidea Prote^hinoidea 



Echinoidea Holothuroidea 



Crinoidea ' 



Blastoidea 



We shall hazard the prophecy that if ever pre -Cambrian 

 Echinoderms are found, there will be amongst them small 

 stalked forms which may be superficially classed with " Cystids," 

 but which are in reality the fixed ancestors of Asteroidea. They 

 should have an irregular skeleton, and be devoid of arms, which 

 are secondary formations ; but they should indicate, by the prox- 

 imity of the mouth to the stalk and by the relation to the stalk 

 of the grooves for the podia, that they have diverged from the 

 Pelmatozoan stock, and are the ancestors of Eleutherozoa. 



