CONTENTS. 



CHAPTER XVII. 



PAGE 

 OF THE CLASS OF GASTEROPODA 361 



ORDER I. PULMONEA ....... 370 



ORDER II. NUDIBRANCHIATA 373 



ORDER III. INFEROBRANCHIATA 375 



ORDER IV. TECTIBRANCHIATA ib. 



ORDER V. PECTINIBRANCHIATA . . . . .377 



ORDER VI. TUBULIBRANCHIATA 386 



ORDER VII. SCUTIBRANCHUTA ib. 



ORDER VIII. CYCLOBRANCHIATA 387 



CHAPTER XVIII. 



OF THE LAMELLIBRANCHIATE CONCHIFERA 390 



ORDER I. OSTRACEJE 397 



ORDER II. PECTINID* 401 



ORDER III. MARGARITACE^S 402 



ORDER IV. MYTILACRE 405 



ORDER V. UNIONID*: 407 



VI. ARCACEJE 408 



VII. CHAMACRB 409 



ORDER VIII. CARDIACE* 411 



ORDER IX. SOLENID^ . .... 413 



ORDER X. INCLUSA 414 



CHAPTER XIX. 



OF. THE CLASS OF PALLIOBRANCHIATA ...... 420 



CHAPTER XX. 



OF THE CiASS OF TUNICATA . .... 423 



CHAPTER XXI. 



GENERAL CHARACTERS OF RADIATA 435 



