CONTENTS. XI 



!• A G E 



lopods, lOG : IV'ctiiiibranchcs, lUG — 108 : Tiibulibianclios, 1U8 : 

 Scutibranches, 108 : Cyclobranchcs, 108 : Acephales tcstaccs, 108 — 

 110: Aceplialcs sans coquillcs, 110 : Bracliiopods, 110, 111. . . 99 



LETTER Vlll. 



The locomotion of the Mollusca : connection between the shell and 

 animal, 113 : the muscles, 114. — Swimmers : the Pteropods, 114 — 118 : 

 tiie Heteropods, 118, 119: the Ccphalopods, 119, 120: the Nautilus, 

 121 — 123: the Paper Nautilus, or Arg-onaut, 123 — 125: the Salpse 

 and Pyrosomfc, 125, 126. — Crawlers : the CejAalopods, 126 : the 

 Gasteropods, 126— 132: the lanthina, 132—134: the Litiopa, 134 : 

 Bivalve Mollusca, 135 : Bivalvular Leapers, 136 : Bivalvular Swimmers, 

 137, 138. . . . . . . . .112 



LETTER IX. 



Burrowing and stationary Mollusca : arenacolous,139 — 141 : byssife- 

 rous, 141 — 145 ; cemented and pedunculated, 145, 146 : stationary 

 Gasteropods, 146, 147 : tlie Patella, 147, 148. . . .139 



LETTER X. 



Boring Mollusca and nest-builders : saxicavous Mollusca, 149, 150 : 

 their mode of operation by boring, 151 : by a solvent, 151, 152 : Mr. 

 0.sler's theory, 152 — 157 : Mr. Garner's theory, 157 : Mr. Hancock's 

 discoveries and theory, 157 — 162 : saxicavous Gasteropods, 162 : snails 

 are doubtful borers, 162 — 164: nest-builders and carriers, 164 — 166: 

 classification of Mollusca from differences in their power of locomotion, 

 167. ......... 149 



LETTER XI. 



Their system of aqueducts : variation of size in the same individual, 

 168, 169 : how produced, 169 — 171 : description of the aquiferous 

 system, 171—174. . . . . . .168 



