CONTENTS. 



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Title 1 



Preface a 



Contents 9 



The Palaeozoic Reticulate Sponges constituting the Family Dictyospongidse 11 



Introductory 13 



Preliminary remarks 13 



General Observations on the Sponges 14 



Anatomy 14 



Form 16 



Individuality 16 



Mode of Attachment 16 



The Siliceous sponges. Skeletal structure 17 



Taxonomy 20 



Symbiosis 21 



Affinities of the Dictyospongidse 22 



Family Dictyospongidse 29 



Structure of the Skeleton 29 



Variations and Genetic Relations of form 33 



Modes of Preservation 36 



Habitat and Mode of Occurrence 37 



Historical ; Bibliography 41 



Classification 52 



Synoptic List of Genera and Species 54 



Tables showing the Geologic Distribution 00-62 



Descriptions of Genera and Species 63 



Species of the Silurian , 63 



Species of the Devonian 64 



Species of the Lower Helderberg Group 64 



Species of the Hamilton Group 65 



Species of the Portage Group ,. 68 



Species of the Chemung Group .... 72 



Species of the Psammites du Condroz 147 



Species of the Carboniferous 1 51 



Species of the Waverly Group 151 



Species of the Burlington limestone 1 65 



Species of the Keokuk Group 166 



