Librarkjf U. S. Nat. Museum. ["■ " /(' 



VOL. XXXIX. MAY, 1915. 



Established by BENJAMIN SILLIMAN in 1818. 



THE 



AMEKICAN 



JOURNAL OF SCIENCE. 



Editor: EDWAED 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. 



FOURTH SERIES 



YOL. XXXIX— [WHOLE NUMBER, CLXXXIX]. 

 No. 233— MAY, 1915./^^ 



WITH PLATE VIII. 



NEW HAVEN, CONNECTICUT. 



1915. 



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



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