Preface 



Through the kindness of Mr. C. H. Townsend, Director of 

 the New York Aquarium, I have had opportunity to study many 

 mollusks alive in the fish tanks, and in the remarkable series of 

 balanced aquaria, in charge of JVIr. L. B. Spencer. 



At the American JVIuseum of Natural History, with its mag- 

 nificent collection of shells and its library, every facility for study 

 has been at hand. Particular thanks are due this Museum, the 

 officers of which selected and placed at Mr. Dugmore's disposal 

 the shells from which the color and half-tone illustrations were 

 made. Dr. Louis P. Gratacap, Curator of Conchology, has read 

 the book critically in manuscript, and given me, on all occa- 

 sions, his broad knowledge of the subject and the benefit of 

 his judgment on disputed points. I am also indebted to Mr. 

 Maxwell Smith for painstaking research and for the use of ma- 

 terial from his private collection. 



The plan and nomenclature of this book follow the accepted 

 standard, "The Manual of Conchology," by Tryon and Pilsbry. 

 The shifting of the Cephalopods to fourth place instead of first is 

 justified, I think, in a shell book, because, with the exception of 

 the chambered nautilus, these mollusks are destitute of true, 

 external shells. 



Julia Ellen Rogers. 



New York, February i, 1908. 



