432 cobb: new nematode genera 



added. The anode chamber is filled with acid (1 : 30), the anode 

 inserted and electrolysis started. The temperature is raised to 

 80°C. The current employed is about 8 amperes, while the volt- 

 age drop across the cell is 8 volts. Under these conditions 0.5 

 gram iron is reduced to the ferrous condition in 60 to 70 minutes. 

 After a drop test with thiocyanate shows that reduction in the 

 cathode chamber is complete, the current is stopped, the anode 

 chamber acid is added to the main solution and, after refilling the 

 anode chamber, the electrolysis is continued 10 minutes. At the 

 end of this time the cathode liquid is titrated with permanganate. 

 It will be seen that the method as carried out is not particularly 

 rapid. On the other hand its favorable features are : (1) nothing 

 is introduced into the solution that may carry impurity, and (2) 

 conditions need be defined only within wide limits. The accuracy 

 of the method can only be determined by more extensive compari- 

 son with reductions by other methods. The precision attainable 

 under the best conditions is shown in Table I and II. Under 

 ordinary conditions a precision of better than 1 part in 200 or 

 300 can not be expected until after the method has been more 

 completely developed. 



HELMINTHOLOGY. — New nematode genera found inhabiting 

 fresh water and non-brackish soils. N. A. Cobb, Bureau 

 of Plant Industry. Communicated by Walter T. Swingle. 



The following pages give the characters of twenty-six proposed 

 new nematode genera, as well as those of a type species' for 

 each genus. 



Seventy-three per cent of these genera are found in arable 

 soils in various parts of the world. Nearly half of them have 

 come to light thru a study of the soils of the Arlington Farm of 

 the United States Department of Agriculture, located on the 

 Potomac River, in Alexandria County, Virginia, directly oppo- 

 site Washington, D. C. In the following pages wherever the 

 word '^4rlington" is used, it refers exclusively to this farm. As 

 this farm is close to the District of Columbia, and its soils similar 

 to those of the District, it may be assumed that all the species 



