X CONTENTS 



Page 

 1. The Origix 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 TRILOBITES 

 1. Outline of a Natukal 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. Agnostidse 135 



Family II. Harpedidae 137 



Family III. Trinucleidse 138 



Opisthoparia 138 



Family IV. Conocoryphidse 140 



Family V. OlenidfE 141 



I. Paradoxinse 143 



II. Oryctocephaliuae 145 



in. Oleninse 145 



IV. DikelocephalinaB 145 



Family VI. Asaphidae 145 



I. Asaphidie 146 



II. lUajnidae 14() 



Family VII. Proetidae 147 



Family VIII. Bronteidae 149 



Family IX. Lichadidse 150 



Family X. AcidaspidjE 151 



Proparia 152 



Family XL Encrinuridfe 153 



Family XII. Calymmenidae 154 



