Abstract
The structure of the head and mouth parts of the Streblidae has been very briefly described by Speiser (1900) and subsequently by Muir (1912) in the genera Ascodipteron and Nycteribosca. The description given by the latter author is, however, still incomplete. Having, therefore, collected the necessary material I have re-investigated their structure and compared it with that of the Hippoboscidae and the Nycteribiidae, already described by me elsewhere (1926 and 1928).