This family was covered by Morris (1990) in Orthocerous Weevils: Coleoptera Curculionoidea (Nemonychidae, Anthribidae, Urodontidae, Attelabidae and Apionidae) (Handbooks for the Identification of British Insects) 5:16. The key to British genera now includes keys to species of Cyanapion, Exapion, Ceratapion, Diplapion and Apion. It includes the considerable changes in naming of the genera since Morris' work. See his work for identification to species and detailed information on phenology, distribution and plant associations. Separate translated keys are now available here for genera Perapion and Protapion. There are details of the male and female genitalia in the Protapion key.