CONTENTS. 



CHAP. VII. 



The Phytophagous Gastropods continued. The Turbidae, or Marine 

 Snails - - - ... p a ge 195 



CHAP. VIII. 



The PhytophagouslGastropods concluded. The Haliotida?, or Ear-Shells, 

 and the Naticida?, or Nerits - - - 228 



CHAP. IX. 



On the Aberrant Tribes of the Gasteropoda, namely, the ,Scutibranchia, 

 or Limpets ; the Cyclobranchia, or Chitons ; and the Pteropoda, or 

 Crystal- Shells - - - 241 



CHAP. X. 



On the Order Dithyra, or Bivalve Shells. The Affinities and Analogies 

 of the Unionidae, or River Unios - - - - 253 



PART II. 



A NATURAL ARRANGEMENT OF THE UNIVALVE AND BI- 

 VALVE SHELL-FJSH COMPOSING THE ORDERS GASTERO- 

 PODA AND DITHYRA OF THE CLASS TESTACEA - 2Q5 



EXPLANATION OF TERMS USED IN DESCRIBING THE SHELLS 

 OF TESTACEOUS MOLLUSC A - 39 1 



APPENDIX - - - 405 



