VOL. XLI. FEBKUARY, 1.891. 



Established by BENJAMIN SILLIMAN in 1818 

 THE 



rin &ALQOTT. 



AMERICAN 



JOURNAL OF SCIENCE. 



EDITORS 



JAMES D. and EDWARD S. DANA. 



ASSOCIATE EDITORS 



Professors JOSIAH P. COOKE, GEORGE L. GOODALE 

 and JOHN TROWBRIDGE, of Cambridge. 



Professors H. A. NEWTON and A. E. YERRILL, of 

 New Haven, \ 



Professor GEORGE F. BARKER, of Philadelphia. 



THIRD SERIES. 



YOL. XLI.— [WHOLE NUMBER, CXLL] 



No. 242.— FEBRUARY, 1891. 



WITH PLATES I-X. 



NEW HA YEN, CONN.: J. D. & E.'S. DANA. 

 1891. 



TUTTLE, MOREHOUSE & TAYLOR, PRINTERS. 371 STATE STREET. 



Published monthly. Six dollars per year (postage prepaid). $6.40 to foreign sub- 

 scribers of countries in the Postal Union. Remittances should be made either by 

 money orders, registered letters, or bank checks. 



