﻿jbrary, 
  U. 
  S. 
  IN 
  at. 
  Museum. 
  

  

  

  VOL. 
  XLIII. 
  APRIL, 
  1917. 
  

  

  Established 
  by 
  BENJAMIN 
  SILLIMAN 
  in 
  1818. 
  

  

  THE 
  

  

  AMERICAN 
  

  

  JOURNAL 
  OF 
  SCIENCE. 
  

  

  Editor: 
  EDWARD 
  S. 
  DANA. 
  

  

  ASSOCIATE 
  EDITORS 
  

  

  Professors 
  GEORGE 
  L. 
  GOODALE, 
  JOHN 
  TROWBRIDGE, 
  

   W. 
  G. 
  FARLOW 
  and 
  WM. 
  M. 
  DAVIS, 
  of 
  Cambridge, 
  

  

  Professors 
  ADDISON 
  E. 
  VERRILL, 
  .HORACE 
  L. 
  WELLS, 
  

  

  LOUIS 
  V. 
  PIRSSON, 
  HERBERT 
  E. 
  GREGORY 
  

  

  and 
  HORACE 
  S. 
  UHLER, 
  of 
  New 
  Haven, 
  

  

  Professor 
  HENRY 
  S. 
  WILLIAMS, 
  of 
  Ithaca, 
  

  

  Professor 
  JOSEPH 
  S. 
  AMES, 
  of 
  Baltimore, 
  

  

  Mr. 
  J. 
  S. 
  DILLER, 
  of 
  Washington. 
  

  

  7*\\sonian 
  

  

  FOURTH 
  SERIES 
  

   VOL. 
  XLIII— 
  [WHOLE 
  NUMBER; 
  

   No. 
  256— 
  APRIL, 
  1917 
  

  

  NEW 
  HAVEN, 
  CONNECTICUT. 
  

  

  1917. 
  

  

  THE 
  TUTTLE, 
  MOREHOUSE 
  & 
  TAYLOR 
  CO., 
  PRINTERS, 
  123 
  TEMPLE 
  STREET. 
  

  

  Published 
  monthly. 
  Six 
  dollars 
  per 
  year, 
  in 
  advance. 
  $6.40 
  to 
  countries 
  in 
  the 
  

   Postal 
  Union 
  ; 
  $6.25 
  to 
  Canada. 
  Single 
  numbers 
  50 
  cents. 
  

  

  Entered 
  as 
  second-class 
  matter 
  at 
  the 
  Post 
  Office 
  at 
  New 
  Haven, 
  Conn., 
  under 
  the 
  Act 
  

   of 
  March 
  3, 
  1879. 
  

  

  