ADVERTISEMENT. 



The scientific publications of the United States National Museum 

 consist of two series, the Proceedings and the Bulletins. 



The Proceedings, the first volume of which was issued in 1878, are 

 intended primarily as a medium for the publication of original, and 

 usually brief, papers based on the collections of the National Museum, 

 presenting newly-acquired facts in zoology, geology, and anthro- 

 pology, including descriptions of new forms of annuals, and revisions 

 of limited groups. One or two volumes are issued annually and dis- 

 tributed to libraries and scientific organizations. A limited number 

 of copies of each paper, hi pamphlet form, is distributed to specialists 

 and others interested in the different subjects as soon as printed. 

 The date of publication is printed on each paper, and these dates are 

 also recorded in the tables of contents of the volumes. 



The Bulletins, the first of which was issued in 1875, consist of a 

 series of separate publications comprising chiefly monographs of large 

 zoological groups and other general systematic treatises (occasionally 

 in several volumes), faunal works, reports of expeditions, and cata- 

 logues of type-specimens, special collections, etc. The majority of 

 the volumes are octavos, but a quarto size has been adopted in a few 

 instances in which large plates were regarded as indispensable. 



Since 1902 a series of octavo volumes containing papers relating to 

 the botanical collections of the Museum, and known as the Contribu- 

 tions from the National Herbarium, has been published as bulletins. 



The present work forms No. 93 of the Bulletin series. 



RICHARD RATHBUN, 



Assistant Secretary, Smitlisonian Institution, 

 In charge of the United States National Museum. 



WASHINGTON, D. C., June 8, 1916. 



in 



