Peter Barnard in Identifying British Insects and Arachnids: An Annotated Bibliography of Key Works writes about the beetle family Cryptophagidae that there is "no comprehensive key work to the group yet available"
This is a first attempt to make a contribution to this gap in knowledge on the web. I've just published an illustrated key to the genera of Cryptophagidae which includes keys to species of all the genera except the big two, Atomaria and Cryptophagus. I am working on translations of these as I can and will publish them in due course. The key is published at https://sites.google.com/site/mikesinsectkeys/Home/keys-to-coleoptera/cryptophagidae
As always if you use this key (or any on the site) please let me have your comments so that I can improve their quality and clarity.