x CONTENTS 



PAGE 



1. THE ORIGIN AND SIGNIFICANCE OF SPINES Con- 

 tinued 



Categories of Interpretation 93 



Spinosity a Limit to Variation 93 



Spinosity the Paracme of Vitality 97 



Conclusion 99 



References 102 



II. STRUCTURE AND DEVELOPMENT OF TRILOB1TES 

 1. OUTLINE OF A NATURAL CLASSIFICATION OF THE 



TRILOBITES 109 



Introduction 109 



Previous Classifications 110 



Rank of the Trilobites 114 



Comparative Morphology of Crustacea 115 



Morphology of the Cephalon ...117 



Principles of a Natural Classification 119 



Application of Principles for Ordinal Divisions . . . 121 

 Application of Principles for Arrangement of Families 



and Genera 125 



Diagnoses and Discussions 130 



Arrangement of the Families of Trilobites 131 



Diagnoses and Discussions of Orders and Families . . 134 



Hypoparia 134 



Family I. Agnostidas . 135 



Family II. Harpedidae 137 



Family III. Trinucleidaa 138 



Opisthoparia 138 



Family IV. Conocoryphidae 140 



Family V. Olenidas 141 



I. Paradoxinse 143 



II. Oryctocephalinae 145 



III. Oleninae 145 



IV. Dikelocephalinae 145 



Family VI. Asaphidse 145 



I. Asaphidas 146 



II. Illsenidae ' 146 



Family VII. Proetidse 147 



Family VIII. Bronteidae 149 



Family IX. Lichadidse 150 



Family X. Acidaspidas 151 



Proparia 152 



Family XI. Encrinuridse 153 



Family XII. Calymmenidae 154 



