AD\^RTISEMENT. 



The scientific publications of the United States National Museum 

 consists 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 

 anthi'opology, including descriptions of new forms of animals and 

 revisions of limited groups. One or two volumes are issued annually 

 and distributed to libraries and scientific organizations. A limited 

 number of copies of each paper, in pamphlet form, is distributed to 

 specialists and others interested in the different subjects as soon as 

 printed. The date of publication is recorded in the tables of contents 

 of the volume. 



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 (occa- 

 sionally in several volumes), faunal works, reports of expeditions, 

 and catalogues of type-specimens, special collections, etc. The ma- 

 jority of the volumes are octavos, but a quarto size has been adopted 

 in a few instances in which large plates were regarded as indis- 

 pensable. 



Since 1902 a series of octavo volumes containing papers relating 

 to the botanical collections of the Museum, and known as the Con- 

 tributions from the National Herharium, has been published as 

 bulletins. 



The present work forms No. 117 of the Bulletin series. 



William deC. Ravexel, 

 Administrative Assistant to the Secretary, 

 In charge of the United States National Museum. 



Washington, D. C, March 19, 1921. 



