SEP 6 1900 



THE DEVELOPMENT AND PHYLOGENY OF 



PLACENTICERAS. 



BY JAMES PERRIN SMITH. 



Stanford University, California. 



CONTENTS. 

 Plates XXIV-XXVIII. 



Page. 



Introduction 182 



Types of Development 182 



Primary and Secondary Larvae 183 



Unequal Acceleration 185 



Retardation 187 



Groups Available for Correlation 190 



Coslenterata 191 



Echinodennata 191 



Brachiopoda 192 



Mollnsca 192 



Crustacea 193 



Affinities of Placenticeras and Hoplites 193 



Phylogenic Table of Placenticeras and Associated Genera 202 



Placenticeras californicum Anderson ( MS. ) 203 



Larval and Adolescent Stages 205 



Placenticeras pacificum, sp. nov 207 



Larval Stages 210 



Phylembryonic Stage 210 



Ananepiojiic • 211 



Metanepionic 212 



Paranepionic 213 



Adolescent Stages 214 



Ananeanic — Cymbites Stage 214 



^goceran Stage 216 



Perisphinctoid Stage 216 



Metaneanic — Cosnwceras Stage 217 



Paraneanic — Hoplites Stage 220 



Ephebic or Adult Stage 221 



Table of Cross-section of Placenticeras pacificum 224 



Table of Stages of Growth of Placenticeras pacificum. . 224 



Conclusion and Summary of Results 226 



Bibliography 230 



Explanation of the Figures 232 



I 181 I August 4, igoo. 



