Vol. VI No. 21 



December 19, 1916 



JOUENAL 



OF THE 



WASHINGTON ACADEMY 



OF SCIENCES 



BOARD OF EDITORS 

 William R. Maxon N. Ernest Dorset Adolph Knopf 



NATIONAL MUSEUM BUREAU OF STANDARDS GEOLOGICAL SURVEY 



PUBLISHED SEMI-MONTHLY 

 EXCEPT IN JULY, AUGUST, AND SEPTEMBER, WHEN MONTHLY 



WASHINGTON ACADEMY OF SCIENCES 



OFFICE OF PUBLICATION 



WILLIAMS & WILKINS COMPANY 



BALTIMORE, MD. 



Entered as second-class matter July 14, at the post office at Baltimore, Maryland, under the Act of 



July 1G, 1894 



