2 BULLETIN 140, UNITED STATES NATIONAL MUSEUM 



as the present one will facilitate identification of nematodes and 

 stimulate interest in them. 



The author has attempted to make a critical study of the species 

 in the assignment of them to genera. This is at times very difficult, 

 due to inadequate descriptions. For the same reason the keys which 

 have been given for all groups dealt with, from species up to orders, 

 in many cases fall far short of what could be desired. If authors in 

 describing new species of nematodes would hold to certain minimum 

 essentials in the details of the description, comparable data would be 

 available and the making of a key a comparatively easy task ; when, 

 however, one writer confines his attention to the head and another 

 to the tail of their respective worms it is often not only difficult but 

 impossible for a third person to recognize and distinguish the one 

 from the other. 



Viewing the classification of nematodes as a filing system, and as 

 such capable of being enlarged or contracted to suit the convenience 

 of workers, the present writer has made several new groups that 

 seemed necessary, or at least desirable, for coordination. Classifica- 

 tion has evolved upward from species to genera, genera to families, 

 etc., and as the number of forms increases below, new groups are 

 needed above in order to indicate and maintain relative rank. The 

 present writer has accordingly made several new families and super- 

 families and has recognized the suborders as previously made by 

 various authors and the two orders as made by Ward. 



Only seven neAV species have been described ; this part of the work 

 is considered quite subordinate to the assembling and systematic 

 arrangement of published material. Redescriptions have been given 

 of several species in which details were lacking and new names to 

 two previously described species. 



The Filarioidea and Trichurata have not been dealt with here; 

 both these groups have a large number of species in birds, but they 

 are so poorly known and demand such a great amount of study that 

 it was deemed inadvisable to attempt to deal with them at the 

 present time. 



The main emphasis has been placed upon the Spiruroidea. as that 

 is the group involving the largest number of species and the greatest 

 variety in respect to genera and families of the nematodes of birds. 

 It may be regarded as primarily and characteristically a group of 

 bird parasites, the spirurids in other host groups making a much 

 smaller group. This is due largely to the fact that the spirurids 

 are heteroxenous nematodes, which, unlike the great majority of 

 the Filarioidea. except in rare instances, have intermediate hosts 

 that are eaten. Small arthropods, such as entomostracans and in- 

 sects, are the usual intermediate hosts of spirurids in the cases where 



