yi INTRODUCTION. 



Tilt' jircsciil volume consists, therefore, of a reprint from these 

 stereotype plates, with the original pjiging at the top, and the 

 Smithsonian paging at the bottom ; and of a general index of 

 species. 



The index was prepared (at the expense of the Smithsonian 

 Institution) by Mr. E. Taylor, Student at McGill College. It 

 includes not only the present volume but all my previous English 

 publications on the subject, of which the principal are the First 

 British Association Report and the British Museum Mazatlau 

 Catalogue. All references to these works )wf repi'inted have 

 the page-number prefixed by a Roman Capital (O to X), by 

 which they can be at once distinguished from the simple num- 

 bers which refer to the foot-page in this volume. Students who 

 want an index to the First Report will fix the eye on the initial 

 O; to the Mazatlan Catalogue on 1*. 



In an accompanying list will be found an enumeration of all 

 my papers published in European journals relative to American 

 conchology, and for the most part reprinted in the present col- 

 lection. In this, however, is not included any of the contribu- 

 tions to American serials, as the Journal of the Academy of 

 Natural Sciences of Philadelphia, the Proceedings of the Cali- 

 fornia Academy, or the American Journal of Conchology. 



My principal object in the preparation of these works has been 

 to make out and compare the writings of previous naturalists, so 

 that it might be possible for succeeding students to begin where 

 I left oft", without being obliged to waste so large an amount of 

 time as I have been compelled to do in analyzing the (often inac- 

 curate) work of their predecessors. 



As the work of previous writers, whether satisfactory or other- 

 wise, is duly tabulated in my Reports, so that others may judge 

 of its value as well as I, it is not fair (as is often done) to quote 

 from these Reports as on my authority. I was simply the his- 

 torian, not the original writer. In the First Report I was a 

 novice in the scientific world, and rarely ventured on criticisms ; 

 in the second, I allowed myself with more confidence to state 

 my own conclusions, because I found that others had not enjoyed 

 the remarkable facilities of comparing types which fell to my lot, 

 and which (in many instances) cannot be renewed. Since that 

 time, Nuttall, Gould, Rich, Judge Cooper, and especially ITugh 

 Cuming, have been called to another world ; their collections 



