GENEEA ANl) GROUPS OF THE ECHINOIDEA. 59 



I. Subfamily Diadematince. Ambulacral plates compound, near 

 the ambitus ; the pairs of pores in simple "vertical series or in 

 arcs of threes. 

 I. Genus Diadema (syu. Pseudodiadema). 



Subgenera Centrostephanus, Microdiadema, Diademopsis, 

 Hemipedina, Echinodiadema. 

 II. Genus Placodiadema (syn. Plesiodiadema). 



Genus incertse sedis. Progonechinus. 



