PAGE 



February and March, 1912 547 



July, 1912 547 



August to October, 1912 548 



November, 1912 548 



The effect of a dam on dissolved gases 549 



Seasonal phases of chemical condition 550 



Additional data upon the river sludges 551 



Explanation of plates 573 



ARTICLE XI. VEGETATION OF SKOKIE MARSH. BY EARL E. 



SHERFF. (12 Plates) August, 1913 575-614 



General features of Skokie Marsh 576 



General features of the marsh vegetation 577 



Certain ecological factors 5S0 



Subterranean organs and their interrelationships 583 



Summary and conclusions 591 



Annotated list of plant species 592 



Literature cited bii 



Explanation of plates 613 



ARTICLE XII. SOME NEW ILLINOIS ENCHYTR^ID^. BY 

 FRANK SMITH, A.M., AND PAUL S. WELCH, Ph.D. (5 Plates) 

 August, 1913 615-636 



Pridcricia Michaelsen 615 



Fridcricia Urnia n. sp 616 



Definition 61O 



Affinities 617 



External characters .617 



Internal characters v 617 



Fridcricia tcncra n. sp 620 



Definition 620 



Affinities 621 



External characters 621 



Internal characters 622 



Fridcricia agilis Smith 623 



Definition 623 



External characters 624 



Internal characters 624 



The function of the chylus cells in Fridcricia 626 



Marionina ^lichaelsen 628 



Marionina forbescc n.sp 629 



External characters 630 



Internal characters 631 



Literature cited 634 



Explanation of plates 635 



