184 Clark — Proposed Division of the Phylum Echinodermata . 



from the ophiuroids and asteroids, which are also similarly 

 closely related. The holothurians belong with the former group. 

 Detailed anatomical evidence of this will shortly be published 

 in the American Naturalist. 



The following is proposed as the arrangement best showing 

 the interrelations of the classes in the phylum Echinodermata 

 in the light of the most recent knowledge: 



PHYLUM ECHINODERMATA. 



I. Sub-phylum Echinodermata Hp:teroradiata. 



1. Class Pel matozoa. 



a. Sub-class Crinoidea. 



b. Sub-class Cystoidea. 



c. Sub-class Blastoidea. 



2. Class Erhinoidea. 



3. Class Holothuroidea iBohadschoidca). 



n. Sub-phylum Echtnodehmata Astroradiata. 



1. Class Ophivroidea. 



2. Class Asteroidea. 



