cobb: new nematode genera 433 



found at Arlington occur in the District of Columbia, and prob- 

 ably also in adjacent parts of Maryland and Virginia. 



Nine-tenths of the proposed genera are due to the discovery 

 of new forms; the others are proposed on the basis of later in- 

 vestigations of species earlier made known, and assigned, with 

 some doubt, to existing genera. A number of the genera are 

 known to the writer to contain numerous species, and in such 

 cases it has been possible to select as a type species one already 

 known to be thoroly representative of a well defined generic group. 



Most of these genera are injurious to vegetation, and many 

 of them contain species that are very abundant and widespread. 

 The morphology, physiology, life-history, distribution and eco- 

 nomic relationships of the species belonging to these genera will 

 be treated in a separate publication. 



The following diagram illustrates the nature of the formula 

 used in the tabulation of the various necessary measurements: 



„ ,■■- 88^ 



Fig. 1. Diagram of the descriptive decimal formula used for nematodes; 6, 7, 8, 

 10, 6 are the transverse measurements, while 7, 14, 28, 50, 88 are the correpond- 

 ing longitudinal measurements. The formula in this case is : 



7. 14. 28. 50. 88. 

 6. 7. 8. 10. 6. 



The unit of measurement is the hundredth part of the length 

 of the body, whatever that may be. The measurements become, 

 therefore, percentages of the length. The absolute length is 

 ^iven in millimeters as a final non-paired term. 



The measurements are taken with the animal viewed in profile; 

 the first are taken at the base of the pharynx, the second at the 

 nerve-ring, the third at the cardiac constriction or end of the 

 neck, the fourth at the vulva in females and at the middle (M) 

 in males, the fifth at the anus. 



Owing to the fact that the measurements vary somewhat with 

 varying technique, a brief note as to the method of fixation and 



