Mycetophagidae
Six genera and 13 species constitute the British list but two of these no longer occur: Litargus balteatus Le Conte included from a single 19th century Nottinghamshire record and Mycetophagus fulvicollis Fab. with several 19th century records from a single Perthshire locality. Eulagius filicornis (Reitter), an introduction established in the Reading area, was added to the list by Harrison (1996).

Elongate and finely pubescent beetles associated with fungi, mostly monophagous or oligophagous, with several characteristically marked species that will soon become familiar.
2-6mm. Antennae 11 segmented (cf. Ciidae) with basal segment sometimes larger, segments 3-6 quadrate or elongate and 7-11 variously transverse or enlarged forming a loose club. Glabrous or with short pubescence and inserted in front of eyes, separation much wider than length of basal segment. Palpi much shorter than antennae. Mandibles bifid at apex and not produced forward (cf. Heteroceridae). Head broadest at eyes, never deflexed. Sometimes with short outstanding setae behind eyes. Pronotum transverse (almost quadrate in Triphyllus) with sides narrowly explanate, not or only slightly narrower than base of elytra, hind margin generally sinuate. Lateral margins smooth or finely crenulate, not serrate and without tubercles or callosities. Without raised lines (cf. Biphyllidae) or tubercles, sometimes with basal fovea and when present these are simple i.e. not bordered or ridged on outerside (cf. Symbiotes), without outstanding setae. Elytra entire and covering abdomen. Elongate or oval and with strongly punctate striae (Mycetophagus) or randomly punctate, often with lighter markings or patterned. Underside more or less flat, upperside moderately convex (cf. Byturidae, see tarsi). Femora not elongate, often not visible in set specimens. Tibiae without teeth and with small apical spines on inner side. Tarsi about equal in length to tibiae , 4-4-4 in female, 3-4-4 in male. Last segment shorter than the rest together. Claws simple, not abruptly bent or toothed. Upper surface with fine, usually recumbent, pubescence and sometimes with scattered larger setae on elytra (Mycetophagus) or with setae forming striae (Typhaea).

A key to genera is given in the IDAids

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

Mycetophagus atomarius
 

Mycetophagus punctatus

Mycetophagus punctatus
 

Mycetophagus quadripustulatus

Mycetophagus quadripustulatus

Mycetophagus quadripustulatus

Mycetophagus quadripustulatus

Mycetophagus quadripustulatus