ADVERTISEMENT. 



TriE prcscMit series, entitled "Smithsonian Miscellaneons Col- 

 lections," is intended to embraee all the pnblications issned directly 

 by the Smithsonian Institution in octavo form ; those in quarto con- 

 stituting the "Smithsonian Contributions to Knowledge." The 

 quarto series includes memoirs embracing the records of extended 

 original investigations and researches resulting in what are be- 

 lieved to be new truths, and constituting positive additions to the 

 sum of human knowledge. The octavo series is designed to con- 

 tain reports on the present state of our knowledge of particular 

 branches of science : instructions for collecting and digesting facts 

 and materials for research: lists and synopses of species of the 

 organic and inorganic world : museum catalogues : reports of ex- 

 plorations : aids to bibliographical investigations, etc., generally 

 prepared at the express request of the Institution, and at its 

 expense. 



The position of a work in one or the other of the two series will 

 sometimes depend upon whether the required illustrations can be 

 presented more conveniently in the quarto or the octavo form. 



In the Smithsonian Contributions to Knowledge, as well as in the 

 present series, each article is separately paged and indexed, and 

 the actual date of i1?s publication is that given on its special title- 

 page, and not that of the volume in which it is placed. In many 

 cases, works have been published, and largely distributed, years 

 before their combination into volumes. 



While due care is taken on the part of the Smithsonian Insti- 

 tution to insure a proper standard of excellence in its publications, 

 it will be readily understood that it cannot hold itself responsible 

 for the facts and conclusions of the authors, as it is impossible in 

 most cases to verify their statements. 



JOSEPH HENRY, 



Secretari/ S. I. 



( vii ) 



