A small family of four saproxylic beetles being found in or on wood-decay fungi. There are three British species in the genus Tetratoma and they have been joined by Hallomenus binotatus which until recently was regarded as a member of the family Melandryidae. Identification is straightforward. All four are covered by Buck’s (1954) RES Handbook (which has Hallomenus as a member of the Melandryidae) but the best key to use now is by Richard Wright in Beetle News Volume 3, Issue 3, October 2011 (PDF, 252Kb). Richard’s key includes photos of all four species.
Buck, F.D. (1954). Coleoptera (Lagriidae, Alleculidae, Tetratomidae, Melandryidae, Salpingidae, Pythidae, Mycteridae, Oedemeridae, Mordellidae, Scraptiidae, Pyrochroidae, Rhipiphoridae, Anthicidae, Aderidae and Meloidae). Handbooks for the identification of British insects, vol. V, part 9. London: Royal Entomological Society. Out of print but should be available as a download from here before much longer.