CONTENTS 



Page 



Introduction i 



Acknowledgments 2 



Evolution 4 



Ambulacral pores 4 



Phyllodes 7 



Petals 10 



Apical system 11 



Bourrelets 12 



Periproct 13 



Peristome 13 



Tuberculation 14 



Shape 14 



Size 14 



Summary of evolutionary trends 15 



Phylogeny 15 



Distribution in time 20 



Ecology 21 



Systematics 22 



Literature cited 229 



Explanation of plates 241 



Index .- 257 



