The following key to British genera, adapted from the literature, will help to describe the family.

1. Antennae filiform, distally thickened or with a club consisting of more than three segments. 2.
-- Antennae with a three segmented club 3.
2. Antennae filiform, elytra with characteristic dark markings; a well developed triangular mark basally and a broad U-shaped band parallel to the margin. Upper surface with long, conspicuous pubescence. 3.3-3.8mm. Eulagius filicornis (Reitter)
Recorded from Britain by Harrison (1996) in 1993 from Reading, Berkshire.
-- Antennae thickened or with club consisting of more than three segments. Elytra with distinctly punctured striae and coloured marks. 3-6mm. Some species with finely crenulate pronotal margins (X40) Mycetophagus Hellwig
3 (1). Entire beetle depressed. Pronotum broadest at base, broader than elytra at shoulders, hind angles sharp, right angled. Lateral margin strongly rounded to narrow front margin, without crenulation. Upper surface black, elytra with well-defined yellow marks including subhumeral and transverse subapical. Legs yellow to almost black. 2.4-2.8mm. Antennae with distinct three segmented club Litargus Erichson
Two species on the British list. L.balteatus Le Conte thought to be extinct.L.connexus (Geoffroy in Fourcroy, 1785) is widespread in central and eastern England, rare in the west. Larvae develop in Daldinia concentrica on Fraxinus, adults under the bark near fruiting bodies.
-- Distinctly convex and usually strongly so. Pronotum finely crenulate (X40). Elytra without transverse subapical mark. 4.
4 (3). Elytra finely punctured, parallel, at middle as wide as base of pronotum. Sometimes with rows of erect pubescence giving the impression of striae. Entire beetle dark yellow or yellowish-red. Antennae with distinct three segmented club. 2.5-3mm. Typhaea Stephens
One species, T.stercorea (L.) The hairy fungus beetle. Widely distributed and often common among vegetable refuse.
-- Elytra very strongly punctate, not parallel, broadest in front of middle and wider than pronotum. 5.
5 (4). Pronotum with basal fovea and hind margin almost straight. Antennal segment 5 longer than 4 or 6, 9 and 10 strongly transverse forming an abrupt three segmented club. 2.2-2.8mm. Dark, almost black, with sides of pronotum and elytra to some extent reddish-yellow, elytra sometimes completely dark. Elytra closely and moderately strongly punctured, pubescence recumbent and short. Pseudotryphyllus Reitter
One species, P.suturalis (Fab.) Widespread over eastern England and southern Scotland. Associated with bracket fungi on wood, generally Polyporus and Laetiporus.
-- Pronotum without fovea, basal margin bisinuate. Antennal segments 4-6 equal, 9 and 10 quadrate and much longer than 8, forming a three segmented club. Head and pronotum dark red, elytra black with base and an apical mark light red. Upper surface very strongly punctured and with long, semi-erect pubescence. 3.5-4mm. Triphyllus Dejean
One species, T.bicolor (Fab.) Local in lowland wood pastures and ancient woodland across Britain, absent from the west. Associated with freshly fruiting fungi on Oak and Beech.
Joy's handbook covers the British species but for Eulagius. Vogt, H. in Freude, H. Die Kafer Mitteleuropas 7:191-196 includes excellent line drawings of Triphyllus, Litargus, Typhaea and M.quadripustulatus as well as antennae and aedeagus of Mycetophagus spp. Eulagius is not included.

Harrison, T.D. 1996. Eulagius filicornis apparently established in Britain. Coleopterist 4:65-67