INTRODUCTION. 13 



such value as it may possess inheres. Experience has shown that 

 check-lists, however imperfect in themselves, are extremely useful in 

 stimulating faunal research, and it is in the hope that this result will 

 be secured that the compiler finds his chief return for the labor and 

 time expended upon a confessedly imperfect production. 



Having been for some time engaged in a revision of the general sys- 

 tem for the classification of Pelecypods, which will shortly appear in 

 print, the revised classification has been used in the List of Pelecypoda, 

 Table II, as far as it is applicable thereto. 



The writer is under particular obligations to Prof. Alexander Agassiz, 

 as already stated, and also to Professor Verrill and Miss Bush for the 

 use of drawings and for an unpublished list of shallow-water mollusks 

 obtained near Cape Hatteras, which has added to our list several spe- 

 cies and confirmed several others about which I had felt some doubt. 

 The different sources of the figures will be found acknowledged under 

 the "Explanation of the Plates" in each case. 



In conclusion, the writer expresses his obligation to the gentlemen 

 whose writings have been laid under contribution; to all who have 

 facilitated his endeavors to form a representative collection of this mol- 

 lusk fauna, for the use of students in the National collection ; and to Dr. 

 E. E. C. Stearns, of the U. S. Geological Survey, for invaluable personal 

 assistance. The compiler solicits correspondence from all interested, 

 toward the improvement of this catalogue and especially series of the 

 local shells from any point on the coast which may shed light on the 

 geographical distribution of the species. Such correspondence or ma- 

 terial may be addressed to the Curator of the Department of Mollusks at 

 the U. S. National Museum, Washington, D. C., or in care of the Smith- 

 sonian Institution. 



WASHINGTON, May 15, 1889. 



