2 PROCEEDINGS OF THE JWATIONAL MVSEUil. vol. 50. 



Messrs. Warren and Donthitt are still in my possession undescribed, 

 as the restudy of old forms left too little time for the description of 

 all the new ones. 



INTRODUCTION. 



There are several reasons Avhich led to the writing of this paper. 

 In the first place, it has always appealed to the writer as a consider- 

 able service to scientists, even though to a less degree a contribution 

 to science, to gather together under one cover the scattering notes 

 and papers of other writers, often concealed under non-significant 

 or even misleading titles. Few reprints or separates ever come to 

 hand Avhich are more acceptable than these. They are easily kept in 

 mind and are an incentive to study material which would otherwise 

 be laid aside owing to the difficulties involved in getting together the 

 literature necessary for an adequate study of that material. Too 

 little of this sort of work is done, possibly for the reason that sys- 

 tematic work of this character is thankless work. The frequent 

 criticism " mere compilation " carries a slur which is rather poor 

 return for the months of studying over poor descriptions and the 

 tracing of obscure references. 



In the second place, it has seemed desirable to cover in some sys- 

 tematic way the genera, species, and groups of nematodes involved in 

 this study in such a way that the work of other writers might be 

 rendered available to the average worker. This work of systematiz- 

 ing and correlating is neglected by some of our best workers. In fact, 

 only a rather small minority apparently deem it necessary or desir- 

 able to indicate in the publication of a new species or genus the re- 

 lationships to other species or genera or the family to which it be- 

 longs. More than that, many excellent writers publish new genera 

 with merely the name of the type-species to fix the genus, and do 

 this when no respectable diagnosis of the type-species is in existence 

 and no specimens of the type-species are available to the majority of 

 the world's scientific workers. 



A third reason for writing this paper Avas to add descriptions of 

 new genera and species to the forms previously published from ro- 

 dents. This is frankly a subordinate reason. It seems much more im- 

 portant that the preliminary work of compiling and systematizing be 

 done for the benefit of workers in general than that new species be 

 added by the writer. In fact, much new material has been left un- 

 studied in order to benefit by the use of this paper after its appear- 

 ance in print rather than delay publication in order to study that 

 material. 



The reason for treating a group of parasites with reference to a 

 host group rather than with reference to some grouping of the para- 

 sites themselves is that it is often simpler to work from the standpoint 



