VI PREFACE. 



collectors will be supplied with many of these Arctic species. Of those 

 known to science a considerable portion extend southwards to Cape Cod, and 

 are consequently herein described. Our southern limit, on the other hand, 

 will include a considerable number of tropical forms which, dispersed and 

 protected by the warmth of the Gulf Stream, have spread to various por- 

 tions of our southern coast. I could not extend my limits southward to the 

 southern coast of Florida or that of the Gulf of Mexico without including 

 the great West Indian province, which would have enlarged my work to five 

 or six times its present bulk. Tin's portion of our marine molluscous fauna, 

 like that of our Pacific coast, may be advantageously presented in separate 

 treatises. 



It gives mo great pleasure to acknowledge my obligations to many friends 

 for their active interest in my work ; I am particularly indebted to Mr. John 

 H. TiioMso.v, of New Bedford, Mass., and Dr. II. C. Yarrow, of Fort 

 Macon, N. C, for extensive collections from localities rich in species. I 

 have dedicated my work to the memory of the three deeply lamented natu- 

 ralists to whom we are principally indebted for our knowledge of American 

 Marine Mollusca. Two of them, Dr. Gould and Dr. Stimpson, were per- 

 sonal friends, and from the time when they fostered my first efforts in natural 

 science almost to the period of their deaths I never applied to them in vain 

 for assistance and advice in my Conchological studies. 



The generic and specific descriptions used in this book are principally 

 copied from " "Woodward's Manual of the Mollusca," Adams' " Genera of 

 Recent Mollusca," De Kay's " Mollu.sca of New York," Gould's " Inverte- 

 brata of Massachusetts," and from the oi-iginal diagnoses of Say, Adams, 

 Mighels, Stimpson, and others. I thiidv that it is unnecessary to make any 

 apology for using so extensively the language of other writers in preference 

 to preparing original descriptions — the latter course I have adopted when- 

 ever I believed that I could improve or correct the original description. I 

 trust that this general acknowledgment will save me from the reproach of 

 egotism in avoiding the use of cuml)ersome and unsightly quotation marks. 



Ujion the completion of each of my former volumes 1 have promised 

 myself that it should be my last book; that pledge I am again inq)elled to 

 violate. Those alone, who labor in a similar field, can understand how im- 

 peratively science requires her votaries to publish her truths for the instruc- 

 tion of the world. 



GEO. W. TKYON, Jr. 



Ja.nlary 1, 1873. 



