X INTRODUCTION 



Alaimidae of other workers. The bursate parasitic Nematodes, 

 similarly, have, in the course of a few years, risen from the rank 

 of a family, StrongyUdae, to that of a suborder, Strongylata. 

 We have been compelled to reduce the rank of many 

 groups, owing to the false position which the Nematoda must 

 assume in relation to the animal kingdom as a whole if this 

 practice of elevating small groups were continued. Further, 

 the subdivision of groups tends to keep pace with their 

 elevation in rank, and it becomes impossible to find characters 

 of sufficient weight to justify the subdivisions made. Indi- 

 vidual instances of this difficulty will be remarked upon in the 

 appropriate places in the text. 



The generic diagnoses given are not simply extracts from 

 those given by the original authors. We have endeavoured 

 to make use of any subsequent literature which has modified 

 the original diagnosis, and have often taken characters 

 directly from the genotype. We have also tried to define 

 groups in terms which are mutually exclusive, wherever this 

 is possible. It will be seen that the better-known groups 

 usually need only short diagnoses to separate them from each 

 other, whereas the separation of less well-knowTi forms 

 frequently necessitates the use of much longer descriptions, 

 embracing characters of less importance, and, it is to be feared, 

 often of doubtful reliability. 



The quotation of an author's name in conjunction with the 

 name of a subfamily or higher group implies no more than 

 that that author was the originator of the name. 



References to Literature 



At the end of each diagnosis the genotype is specified, and 

 references are given to the more important sources of our 

 information regarding the genus and its genotyi^e. No attempt 

 is made to give a complete bibliography. The abbreviations 

 used to indicate the titles of publications are, in general, those 

 employed in the Zoological Record. 



Synonyms 



In giving the synonymy of generic names we have endea- 

 voured to include all total synonyms, but have not con- 

 sidered it necessary or desirable to mention all the partial 

 synonyms or obvious misspellings. For example, the family 

 Ascaridae, as here imderstood, is roughly co-extensive with 

 the genus Ascaris in its original, wide sense, and if all partial 

 synonyms were to be given, it would have been necessary to 

 include Ascaris in the synonymy of almost every genus in the 

 family. It is doubtful whether this would have served any 

 useful purpose. We have, however, given in square brackets 



