Thymalus

Body size: 4.3–7.5 mm. Body shape convex (not conglobate). Gular sutures wide, subparallel. Frontoclypeal suture absent. Frons: longitudinal groove or depression absent. Cranium ventrally: tufts of long setae at sides absent. Submentum: ctenidium absent. Antennal groove absent. Eyes: size large, lateral. Eyes number: two. Epicranial acumination moderate. Lacinial hooks: two. Galea: shape elongate. Galea: ciliate setae absent. Mediostipes-Lacinia not fused. Palpifer: outer edge even. Mandibular apical teeth number: two, horizontally situated. Mola present. Penicillus (at base) absent. Pubescence above mola or cutting edge absent. Ventral furrow absent. Basal notch moderate. Labrum-Cranium not fused. Epipharyngial sclerite absent. Lateral tormal process: projection projection not developed (all remaining). Ligula: ciliate setae absent. Ligula rigid, not retroflexed, weakly emarginate. Hypopharyngeal sclerite H-shaped. Antenna 11-segmented. Antennal club symmetrical, sensorial fields absent. Front coxal cavities externally open, internally closed. Pronotum transverse. Prepectus absent. Middle coxal cavities open. Elytra: long hairs absent. Epipleuron wide. Elytral interlocking mechanism absent, carinae reduced. Elytral punctation regular, scales absent. Wing: radial cell oblong (or reduced), wedge cell present, cross vein MP3-4 present, cross vein AA1+2-3+4 absent. Front tibiae: spines along side reduced. Hooked spur absent, apical spurs not hooked or weakly hooked. Claws: denticle absent. Parasternites number along ventrites III–VII: one. Spiculum gastrale absent. Tegmen composed of three parts. Larva: Frontal arms V-shaped. Epicranial stem reduced. Endocarina absent. Gular sutures inconspicuous. Gula: anterior apodemes present. Paragular sclerites absent. Hypostomal rods present. Stemmata number: five. Mandibular apical teeth number: two, horizontally situated. Lacinia mandibulae with several small spines. Mola absent. Maxillary palpi 3-segmented. Palpifer present. Pedunculate seta absent. Mala simple. Mala: bidentate protrusion present. Cardo-Stipes partially fused. Cardo: size much smaller than stipes. Ligula present. Labial palpi 2-segmented. Prementum in single part, anterior margin even. Torma: two separate lateral sclerites. Antennal joints 1, 2 transverse. Sensory appendix larger than half of joint 3. Thoracic sclerites pattern (dorsally) 2-0-0. Thoracic sclerites pattern (ventrally) 0+0+0. Trochanter triangular. Abdominal segment IX not divided. Tergite IX flat. Urogomphi present, hooked; median process absent.

Holoarctic: Northern states of USA, Canada, Europe, North Africa, Siberia to China and Japan. Some specimens, probably a new species, have recently been collected in Chinese Sichuan and Yunnan and also in northern Thailand.