logical Illustrations " and " Thesaurus Conchyliorum," Hanley s 

 "Descriptive Catalogue of Eecent Bivalve Mollusca;" and the 

 pages of the various Natural History Journals and Transactions 

 of learned societies contain very many papers of like character 

 and of great importance, such as Lea's "Synopsis of Naiades," 

 Frauenfeld's " Monography of Paludina," Mohrenstern's 

 " Monograph of Rissoidse," Tryon's " Monography of the 

 Order Pholadacea," and " Synonymy of Strepomatidas." There 

 are, besides, hundreds of smaller papers describing species and 

 genera, particularly in the " Proceedings " of the Zoological 

 Society of London, the " Proceedings " and " Journal " of the 

 Academy of Natural Sciences of Philadelphia, and in the three 

 periodical works exclusively devoted to the advancement of 

 Conchology, — the " Malakozoologische Blatter," the "Journal 

 de Conchy liologie," and the "American Journal of Conchology/ 7 



Through the above and other publications, the ten thousand 

 species known to conchologists in 1845 have been increased to 

 over twenty-five thousand, and a much better knowledge of 

 the genera and higher groups has also been attained. It is 

 therefore evident that the publication at the present time of a 

 complete Catalogue of Eecent Mollusca, and their synonymy, 

 based on the critical study of actual specimens-, as well as of 

 descriptions and figures, would be exceedingly useful as a 

 directory for the use of students in this science. 



The Conchological Section of the Academy of Natural Sci- 

 ences of Philadelphia, having nearly twenty thousand well 

 authenticated species under its charge, with access to the many 

 splendid collections belonging to its members, and possessing a 

 library containing nearly every book or pamphlet ever published 

 on the subject of Conchology, has peculiar facilities for publish- 

 ing such a Catalogue. It proposes to avail itself freely of all 

 Catalogues and Monographs heretofore published, giving in 

 such cases full credit to their respective authors, and adding all 

 additional species described to the close of the year 1866. A 

 supplement may be issued in 18Z5, and thereafter every five or 

 ten years, as the number of described species may require it. 

 The work of compilation will be- intrusted, as far as practicable, 

 to those who have made a special study of their respective 

 subjects ; and families or genera will be published as fast as 

 completed, without following any systematic order: the work 

 to include an index to the genera when completed. 



Gentlemen who are willing to assist in the preparation of 

 this great work are requested to make known their wishes ae 

 early as possible. 



The arrangement of the work will be as follows : 



