The above-mentioned families of carnivorous water beetles are taken up here by request of the Editor and Committee, because of the great difficulty most students of Coleoptera, especially if they are beginners, find in identifying any of their captures in these groups, or even in separating the species with approximate accuracy. It is to be feared that with marry it will prove difficult to follow the tables herewith presented; but they have been made as plain as circumstances will allow, and care has been taken to follow the best authorities in the selection of characters supposed to mark the respective species, so that by diligent attention to details the user of the paper may hope to co-relate his collcction with our lists.