PREFACE. 



Iii this volume are contained monographs of two families of POLY- 

 PLACOPHORA : Acantlwehitidce and Cryptoplacidce, with an Appendix, 

 and an Index to the entire group. The APLACOPHORA are then 

 described ; and the remainder of the volume is devoted to the various 

 groups of spiral shelled TECTIBRANCHIATA. 



As it is not proposed to include the NUDIBRANCHIATA^ in the 

 MANUAL, the present volume will complete the First Series, as orgin- 

 ally projected by its illustrious founder. 



The Conchological Section of the Academy of Natural Sciences 

 contemplates the commencement of a Third Series of the Manual of 

 Conchology, to include the Marine bivalve Molluslcs. The continued 

 support of the subscribers to the First Series is earnestly desired, for 

 without their liberal aid this great enterprise cannot be undertaken. 



E. J. NOLAN, M. D.,} 



ANGELO HEILPRIN, ( Publication Committee. 



J. H. BEDFIELD. 



H. A. PILSBRY, Editor. 



