OTRODUCTION. 



After the publication of my first "Report on the present state 

 of our knowledge with regard to the MoUusca of the West Coast 

 of North America," undertaken at the request of the British 

 Association for the Advancement of Science, and printed in their 

 Report for 1856, I visited America in order to arrange the first 

 duplicate series of the great Reigen Collection of Mazatlan Shells 

 which I had presented to the New York State Museum at 

 Albany. It was one of the special objects of my visit to ex- 

 amine the types of previously described species in the United 

 States, that I might compare them with those known in England. 

 Having visited Washington to examine the types of the United 

 States Exploring Expedition (Wilkes'), I was requested to spend 

 the winter of 1859-60 in unpacking and arranging the shells 

 belonging to the National Museum under its charge; and after 

 my return to England I received from time to time the various 

 collections sent to the Institution from the West Coast as they 

 arrived ; all of these were duly compared with the types in the 

 Cumingian and other British collections. 



Being thus in a position to correct a large number of unavoid- 

 able errors in my first Report, and to add a great deal of fresh 

 information from American sources (chiefly obtained through the 

 Smithsonian Institution), I was requested by the British Asso- 

 ciation to embody the material in a " Supplementary Report" on 

 the same subject as the first. Knowing how difficult it is for 

 American students to obtain access to serial publications, I ob- 

 tained permission, in behalf of the Institution, to stereotype this 

 second report, and the papers connected with it, which appeared 

 in the "Proceedings of the Zoological Society," the "Annals and 

 Magazine of Natural History," and the "Journal de Conchy- 

 liologie." 



(V) 



