[In 1919 work on the genus Oneilella was begun by the author and Mr. R. E. Turner. General agreement was reached as to the species represented in the material studied, and a table constructed before Mr. Turner's return to S. Africa. Subsequently all the additional material now dealt with was seen by Mr. Turner, and determined in collaboration.]

The genus Oneilella, Cam. 1904, created for the reception of Cryptus formosus, Brullé 1846, has up to the present remained monotypic. That it contained many more species was evident after an examination of the examples of this genus available in the British Museum collection and in various collections forwarded for identification to the Museum or received through the Imperial Bureau of Entomology. The material so gathered together (over 450 specimens) is, with one doubtful exception, African in source and dates from 1848 onwards. Its analysis has been a matter of some difficulty and has been undertaken chiefly because of the economic importance of some of the species. In the following pages an attempt has been made to summarise our present knowledge of the genus and its parasitism, and to describe such forms as appeared to be new.