Chas. D. Walcott, 



U. S. Geological Survey. 



Wo. 210. Yol. XXXY. JUNE, 1888. 



Established by BENJAMIN SILLIMAN in 1818. 



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. VERRILL, of 

 New Haven, 



Professor GEORGE F. BARKER, of Philadelphia. 



THIRD SERIES. 



YOL. XXXY.-[WHOLE NUMBER, CXXXY.J 

 No. 210— JUNE, 1888. 



WITH PLATES VI AND VII. 



NEW HAYEN CONN.: J. D. & E. S. DANA. 

 1888. 



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