EVOLUTION OF THE BASAL PLATES IN MONOCYCLIC 

 CRINOIDEA CAMERATA. I 



HERRICK E. WILSON 

 United States National Museum, Washington, D.C. 



CONTENTS 



PART I 

 Introduction 



Acknowledgments 



Review of Wachsmuth and Springer's Theory of Basal Plate 

 Evolution 



Review of Certain Phylogenetic Characteristics in Monocyclic 

 Camerata 



Detailed Study of Processes Active in Plate Evolution 



i. Changes Not Primarily Modifying the Relations of Plate Contact and 

 Position 



a) Symmetrical Growth 



b) Reduction of Parts by Absorption 



c) Anchylosis 



PART II 



2. Changes Primarily Modifying the Relations of Plate Contact and 

 Position 

 a.) Reduction and Compensating Growth 



b) Enlargement and Compensating Reduction 



c) Plate Division 



d) Plate Migration 



c) Plate Interpolation 

 f) Anchylosis 

 Anchylosis: Its Antecedents and Consequences 

 i. Anchylosis and Reduction 



2. Delayed Anchylosis 



3. Anchylosis and the Phylogenetic Reappearance of Sutures 

 Development of the Intestine and the Consequent Zones of Potenthl 



Widening 

 Origin of the Anal Plate 



488 



