CAMBRIAN GEOLOGY AND PALEONTOLOGY
II
No. 6.—MIDDLE CAMBRIAN BRANCHIOPODA,
MALACOSTRACA, TRILOBITA, AND
MEROSTOMATA
By CHARLES D. WALCOTT
(With Plates 24 to 34)
CONTENTS
| PAGE | ||||
| Introduction | 148 | |||
| Habitat | 149 | |||
| Character of the shale | 149 | |||
| Mode of occurrence | 151 | |||
| Classification | 153 | |||
| Stratigraphic distribution | 155 | |||
| Structural features | 157 | |||
| Exoskeleton | 157 | |||
| Labrum | 158 | |||
| Segmentation | 158 | |||
| Appendages | 158 | |||
| Alimentary canal | 160 | |||
| Hepatic cæca | 160 | |||
| Origin of Middle Cambrian crustacean fauna | 160 | |||
| Relation to recent crustaceans | 164 | |||
| Survival of the Branchiopoda | 165 | |||
| Class Crustacea | 166 | |||
| Sub-Class Branchiopoda | 166 | |||
| Order Anostraca Calman | 166 | |||
| Family Opabinidæ, new family | 166 | |||
| Genus Opabinia, new genus | 166 | |||
| Opabinia regalis, new species (pls. 27, 28.) | 167 | |||
| Appendages | 167 | |||
| Interior structure | 168 | |||
| Dimensions | 168 | |||
| Female | 169 | |||
| Opabinia ? media, new species | 170 | |||
| Genus Leanchoilia, new genus | 170 | |||
Smithsonian Miscellaneous Collections, Vol. 57, No. 6
145
