The Scaphopoda have hitherto received comparatively little at- 

 tention from either conchological or morphological naturalists. No 

 other molluscan group of like rank and extent exists upon which 

 the anatomical data are so scanty, or restricted to so small a num- 

 ber of species ; and as the Class consists mainly of deep sea dwellers, 

 the list of species now known is doubtless a mere fraction of the 

 grand total of living forms. 



Consonant with the general plan of the " Manual," this volume 

 treats primarily of the "system" of Scaphopods, and the determina- 

 tion of genera and species. A classification of the Dentaliidce based 

 upon features hitherto untried for this purpose is submitted ; and the 

 innovation is made of including a catalogue of fossil species, largely 

 with a view to rectify the current nomenclature and prevent future 

 complications by the duplication of specific names. The labor of 

 collating the references to fossil forms has been, in large measure, 

 accomplished by Dr. Benj. Sharp. 



The work is based upon the collection of the Academy of Natural 

 Sciences, containing a large proportion of known shore species, and 

 upon that of the United States National Museum, including the 

 types of DALL, JEFFREYS, VERRILL and GOULD. 



This great collection, undoubtedly richer than any other in exist- 

 ence in deep sea forms, was, with generosity rarely equalled, placed 

 at my disposal by Prof. William H. Dall, Honorary Curator, and 

 the authorities of the Museum. My most earnest thanks are due 

 to them for this and other courtesies. 



The published works of Dall, Watson and Jeffreys have been 

 freely quoted herein ; and it is to the critical acumen and large ex- 

 perience of these masters of conchological science, transplanted to 

 our pages, that much of their value is due. 



An account of the Aplacophora is also included in this volume, 

 partly for the sake of greater completeness, partly to call the atten- 

 tion of conchologists to this important group, which has doubtless 

 been neglected by many who have opportunities for collecting. 



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