BULLETIN 



OP THE 



[llinois Qtate I aboratory 



OF 



NATURAL HISTORY 



Urbana, Illinois. 



VOLUME V. 



ARTICLE IX. PLANKTON STUDIES. III. ON PLATY- 

 DORLNA, A NEW GENUS OF THE FAMILY VOLVOC- 

 IDsE, FROM THE PLANKTON OF THE ILLINOIS RIVER. 



By C. A. KOFOID, Ph. D. 



Illinois State Laboratory of Natural History, 



UKBANA, ILLINOIS. 



December 28, 1899. 



