xii TABLE OP CONTENTS. 



Page 



CHAPTER IV.— The Summit-Plates 6G 



Homologies of the Summit-Plates 71 



CHAPTER V. — The Hydrospires and Spiracles 76 



A. Historical 76 



B. Descriptive 87 



1. The Hydrospires 87 



2. The Spiracles 96 



CHAPTER VI. — The Zoological Characters of the Blastoidea 113 



Definition of the Pelmatozoa 117 



Definition of the Blastoidea 117 



Rcgulares and Irregulares 122 



Mutual relations of the Genera 125 



DISTRIBUTION. 



CHAPTER VII. — The Geological and Geographical Distribution op the Blastoidea 129 



Silurian forms 129 



Devonian forms 129 



Carboniferous forms 133 



Table showing the Distribution of the Genera of the Blastoidea in 



Space and Time 136 



A Stratigraphical List of all known Blastoids, arranged geographically 137 



Species from the Upper Silurian 137 



Species from the Devonian 137 



Species from the Carboniferous Limestone 140 



CLASSIFICATION. 



CHAPTER VIII. — Descriptions or the Species 146 



Synopsis of the Orders, Families, and Genera 146 



Order Rcgulares 148 



Family Pentremitidse 148 



Definition of genus Pentremites 151 



History of the genus 152 



Genera] characters 154 



Pentremites Godoni, Defrance, sp 157 



var. major, var. nov 160 



var. florealis, Schlotheim, var. . . 160 



var. abbreviatus, Hambachj var. . . . 160 



